From DDO wiki
For those familiar with Dungeons and Dragons, this page tries to assemble a list of differences between version 3.5 pen and paper Dungeons and Dragons, and Turbine's Dungeons and Dragons Online: Stormreach.
- The PnP concepts of darkvision, low-light vision, and portable light sources are gone. In DDO, all characters can see equally well in all areas, and lighting is sufficient for most purposes in most places. However, areas do have varying amounts of light, which affects the difficulty of hiding.
- In DDO, Rest shrines are scattered throughout dungeons. These shrines can be used to heal hit points and spell points once per shrine during an adventure, with the exception of adventures on "casual" mode, where the shrines can be used once every five minutes, and on "normal" mode in quests and in wilderness adventure areas, where the shrines can be used every fifteen minutes. Most rest shrines are adjacent to resurrection shrines, which can be used to resurrect a dead character an infinite number of times. Using a rest shrine restores hit points based on the highest heal skill of a player character near the rest shrine and full spell points.
- In DDO, Wizards, Clerics, Rangers, Paladins, and Druids can change their memorized spells while resting at a rest shrine; spell swapping does not add to the length of time required to use the shrine.
- The number of monsters encountered during an adventure in DDO is significantly higher than PnP. It is easily possible to encounter several dozen monsters over the course of one mission, and some missions have over a hundred monsters. The number of daily spells allotted to a caster at lower levels has been increased to help compensate.
- The penalty for dying is significantly lower in DDO. In PnP the penalty for dying ranges from being forced into a new body with different physical abilities (Reincarnation), loss of one level or two constitution points (for Raise Dead or Resurrection), or expenditure of an enormous sum of money (True Resurrection, Miracle, Wish). In DDO, death results in temporary negative level(s) that will disappear after a set period of time or after resting at a rest shrine. Multiple deaths in relatively rapid succession increase the number of negative levels and, therefore, the length of time needed for the negative levels to wear off. An indirect cost of dying in DDO is the increased cost of repairing gear after the quest; however, damage from death is immune to potential permanent damage.
- The rate of advancement is significantly lower in DDO. While in PnP, every 13-14 encounters results in a level advancement, in DDO there are more encounters than that in one quest and each quest gives only 5-15% of the experience necessary to advance a level.
- In PnP, casters must be careful to avoid damaging themselves and their parties with spells such as Fireball. In DDO, characters cannot damage party members with most spell and combat items unless they are in a PvP area. Occasional spells, such as Grease or Sleet Storm, can impair party member PCs, although they do little to no real damage to hit points.
- Portcullises, cages, gates, and other barriers with spaces in their construction, although see-through, are impervious to spells, arrows, and other forms of attack in most areas of DDO.
- The typical dungeon trap in DDO is a device-based automaton that is local to the effect: once the control box is located, a character with at least one level of rogue or artificer can attempt to disable these traps.
- DDO dungeons frequently feature doors that can be opened only after some certain monster (or set of monsters) dies. If a party member charms one of the key monsters, the party will be stuck until the caster uses the dismiss charm feat, the spell wears off, or the monster makes a save.
- In DDO, there is no movement penalty for being of the dwarven or halfling races, or for wearing heavy armor; however, carrying heavy loads that cause a player to be encumbered does cause a movement penalty. Be encumbered or wearing heavy armor can cause penalties to dodge, jumping, and swimming.
Character Classes and Advancement
- Instead of animal companion and tracking, rangers get both Two Weapon Fighting and archery combat styles, without their limitation of having to wear light or no armor
- PCs receive +20 hp at first level, and full hit-dice thereafter. There are many more monsters than in PnP D&D and those monsters deal more damage and have more hitpoints, so this is simply there to balance that fact out. A good amount of HP is critical in DDO to help you survive a pack of monsters in one piece.
- Sorcerers and Bards can change known spells. By visiting a trainer and paying a fee based on spell level, a single spell is unlearned and replaced with a new spell. After changing a spell, you must wait three days before you may change another.
- Clerics have no domain or identified deity.
- Wizards have no familiar nor opportunity for specialization.
- Rogues get sneak attack bonus on any enemy not attacking them. They also can Hide without cover, although this becomes difficult in brightly lit areas and if no distraction exists.
- Barbarians get Damage Reduction abilities 5 levels sooner than normal. (This compensates them for monsters making a smaller number of more damaging attacks).
- The Paladin's Lay on Hands ability has been significantly boosted to compensate for the higher levels of hit points.
- Paladins may not split up healing between multiple uses of Lay on Hands: they may use it once per day and it heals for the full allotment. (However, certain enhancements can allow them to use Lay on Hands additional times, increasing the amount of damage they can heal.)
- The Paladin's Aura of Good ability provides a bonus of +1 on AC and saves to all allies within its radius of effect which can be further enhanced as ranks (not just levels) are gained.
- Paladin Lay on Hands produces Divine Cure or Repair, as appropriate.
- Multiclass characters never have an XP penalty. However, no character can have levels in more than three classes.
- Characters can reach a maximum of level 30. (This level cap may be increased in later updates.)
- Enhancements provide a new method of character advancement, which bears little resemblance to Action Point usage in Eberron, the Campaign Setting of the world where this game is taking place.
- Prestige Classes appear in the form of Enhancements typically available at levels 6, 12, and 18.
- New attacks gained from higher BAB gives bonus to attack rolls 5 points higher than the previous attack instead of 5 points lower.
- Halflings have lost their penalties of slower running speed and smaller weapon sizes. Their advantage of fitting in smaller spaces is also gone.
- Elves are light-skinned primarily in the game, whereas in Eberron elves could be black, dark brown, and many other varieties of flesh tone.
- Dodge is a percentage chance to miss, not a bonus to AC.
- Combat is real-time, not turn-based. There is not such thing as initiative.
- The concept of attacks of opportunity is gone.
- The condition of being flat-footed is gone. (The Uncanny Dodge class feature, which in PnP gives protection against being flat-footed, is now an active ability that provides temporary bonuses to Dodge and Reflex saves.)
- Most special attacks are not possible. Aid Another, Bull Rush, Charge, Disarm, Grapple, and Overrun are gone.
- Sunder now temporarily reduces an opponent's AC.
- Trip attempts are opposed by a roll modified using the opponent's Balance skill.
- PCs receive a second attack at BAB +1, instead of BAB +6. See attack sequence.
- Nobody can be disarmed. Sunder debuffs AC instead of breaking equipment. (This would make monks relatively less valuable.) although a weapon is automatically unequipped when it has sustained damage (usually from attacking monsters with damage reduction or oozes) equal to its durability and thus requires repair.
- It is possible to block by holding Shift. While blocking, you may not attack (you shield bash instead), but you gain a +2 bonus to AC and, regardless if you have a shield equipped or not, you gain some DR as well.
- Shields provide a bonus to DR when blocking.
- Damage is reduced by Physical Resistance Rating, a new concept that reduces all incoming physical damage by a percentage.
- A miss is not always a miss. Depending on a number of factors, misses on high rolls may produce only Grazing Hits which do only do the base damage of your weapon.
- Two-handed weapons can produce glancing blows that will do damage to targets around the main target of the attack. The Two Handed Fighting feats improve these.
- Coup de Grace  does not exist. Helpless opponents instead take extra damage.
- Regardless of your Swim skill, underwater combat is, in most cases, impossible. (Exception: Into the Deep quest.)
- Melee and ranged attacks have a -4 hit penalty while moving. The feat Spring Attack negates the penalty for melee. The feat Shot on the run negates it for ranged. Note also that tumbling followed by an immediate attack does not give rise to this -4 penalty.
- Heavy and light crossbows reload at the same speed.
- Touching a Black Pudding or other ooze monster does not hurt you, so you may attack with Unarmed Strikes without HP worry. (That will be the most affordable way to kill them). However, items worn on your hands (gloves, rings and possibly bracers) will be affected by ooze acid and require frequent repairs.
- Monsters' regeneration rates (such as on trolls) are significantly higher, however regeneration halts when they have zero hp, regardless of damage type suffered.
- Hill, Fire, and Storm Giants move slower than PC races, instead of faster. All three such giants are about the same height (instead of Storm being much taller)
- Many monsters have significantly more hit points than their PnP counterparts.
- Most monsters have higher attributes than their PnP counterparts.
- Quite common are items providing bonuses of types rarely (if at all) found in PnP. This opens up many possibilities for increasing the skills and abilities, as bonuses of different types stack. For example +6 charisma item (enhancement bonus) and a +3 exceptional charisma (exceptional bonus) will stack for a total of +9 charisma.
- Magic items have a minimum character level prerequisite to equip them. The limit seems to be (Pluses*2)-2 for weapons/armor, or equal to the caster level (for spell triggers). For example, this means that a level 4 wizard cannot use a wand of Fireball, but a barbarian4/sorcerer1 can use it, because his total levels equal the caster level. The Use Magic Device skill cannot defeat this limitation.
- No composite bows built for high strength. Instead, there is the feat Bow Strength, which allows a character to add their Strength bonus to bow damage. Rangers automatically get it at level 1, and fighters can choose it as one of their bonus fighter feats, though anybody can choose it as one of their regular feats.
- All basic weapons have just one physical damage type. Daggers can't Slash, and Morning Stars can't Pierce. However, some high-level unique weapons do more than one physical damage type and so can break multiple kinds of damage reduction. Rahl's Might is an example of this—it does piercing, slashing, AND bludgeoning type damage.
- Polearms don't exist.
- Neither do double weapons.
- No Flails, Nunchaku, Sai, Siangham, Nets, Bolas, or weapon types found only in ancient dusty third-party supplements. However, you can still use a Khopesh.
- There's no discernible difference between a Bow and a Composite Bow except that one has a longer name. This is due to the fact that there aren't range penalties to hit with bows/crossbows/throwing weapons. If you can manage to target it, you can shoot at it.
- Coins are weightless and take up no space, while gems are low-weight and occupy as much volume as platemail armor unless stored in a Gem Bag. (This is the opposite of PnP, where characters will convert coins to gems to make their wealth easier to carry.)
- If your strength is high enough, carrying 10 Greataxes is no more cumbersome than 10 Daggers.
- All magical ammunition and projectile weapons (unless Returning) are immediately destroyed with one use.
- Activating Combat Expertise or just Defensive Fighting takes longer than equipping a shield, and can be interrupted by knockdown.
- It is no longer possible to use multiple trade-BAB-for-something abilities such as Defensive Fighting, Combat Expertise, or Power Attack at the same time.
- You do not get to select an exact number of points of BAB to take off when using Power Attack. Instead, it automatically defaults to your base attack bonus or 5, whichever is lower. If you have enhancements from APs which increase your damage increase beyond 5, this value is always used if it is lower than your BAB (This makes Power Attack less useful.)
- You do not get to select an exact number of points of BAB to take off when using Combat Expertise. Instead, it automatically reduces your attack bonus by 5 and adds 5 to your AC (even if your base attack bonus is below 5).
- Weapon specific feats like Weapon Focus or Improved Critical apply to whole weapon categories (slashing, bludgeoning, piercing, thrown, ranged) and not to single weapons. This means that a two-handed fighter can use the same feats to master both swords and axes, or that a two weapon fighter can master rapier and shortsword together.
- Rapid Shot feat decreases the reload time of missile weapons. It does not grant multiple attacks per click, nor does it impose a -2 to hit penalty.
- Far Shot feat does not exist in DDO; there are no range penalties for ranged/thrown weapons.
- Cleave and Great Cleave have been changed to be active feats that allow you to attack enemies in an arc.
- Several new feats have been added, such as Precision and Slicing Blow.
- Crafting feats are gone (Craft Magic Arms and Armor, Brew Potion, Scribe Scroll). In their place are various other Crafting options including the Full Crafting System, Green Steel Items, and Dragontouched Armor
- Metamagic feats work differently, increasing spell point costs instead of requiring higher-level spell "slots" to use. They are vastly improved in usefulness as a result. Empower, Empower Healing Spell, and Maximize don't add or modify dice numbers any more, but simply add a percentage of overall damage/healing to the spell.
- Skills gone: Knowledge, Climb, Sense Motive, Disguise, Craft, Escape Artist, Sleight of Hand, Use Rope, Gather Information, Profession, Forgery, Animal Empathy.
- The Intimidate skill is used in combat to draw the attention of an enemy (equivalent of "Taunting" in other MMOs)
- The Diplomacy skill works the other way around (enemies targeting you will switch their focus to someone else).
- Use Magic Device has variable difficulty values for wands.
- Tumbling gives an AC bonus during combat but you can't tumble through occupied spaces anymore. Jumping over them replaces this, making Jump more valuable.
- Spellcraft skill increases the damage you deal with spells of Acid, Cold, Electric, Fire, Force and Light types, Heal skill, apart from being usable for first aid (restoring unconscious PCs to 1 hp) and increasing healing on rest, also increases healing you do with spells, Perform, apart from being used for bard songs, also increases your Sonic type damage and Repair, apart from working like Heal skill for Warforged, also increases Repair healing and Rust damage. All of these increases work by adding 1 spellpower in their respective types per skill rank.
- Many skills have been changed so that they are not very useful, and some skills that are not very useful in PnP (such as Jump) have become more useful. See Skill usefulness for details.
- Spells are cast using a spell points system. Prepared spellcasters must still select a limited list of spells to prepare (equal to the number of spells they get to prepare per day in PnP) but they can cast each one many times. There are no bonus spell slots for high ability score.
- Spell points from different classes (e.g. wizard, sorcerer, cleric) stack into one common pool.
- Spellcasters can cast nearly 8 times as many spells before resting. In relation to healing magic, this makes high hitpoints and Fortitude saves relatively less valuable.
- All spells of the same class and level which use materials components, use the same material component. For instance, 3rd level Wizard/Sorcerer spells use balls of bat guano, which in PnP was used only for Fireball. However, some spells, such as Stoneskin and Create Undead have special, more expensive material components.
- Touch attacks are gone, both normal and ranged. Some spells have been given Reflex saves in their place. (This means that high-dex characters are relatively less powerful). The reasoning being that, since we are fighting in a real time, we can avoid them by simply moving. However, if the spell is cast at short range, this can be essentially impossible.
- Spell which are touch range spells in PnP in many cases are not touch range in DDO. Many are expanded to a range over 15 feet; this can be increased by the Enlarge metamagic feat. Some retain the touch range limitation, requiring the player to be right next to the creature they wish to cast on. Examples: Cure Light Wounds is no longer a touch spell, while Shocking Grasp still is.
- Each spell has its own cooldown timer before it can be repeated. That means the fastest way to heal someone is to use a mix of Serious, Moderate, and Light cure spells.
- Major spells gone: Levitate, Spider-Climb, Polymorph, and almost all Divination and Illusion (except Detect Secret Doors and Phantasmal Killer).
- Command only allows "Lay down", not any other action.
- Suggestion functions as charm person, except usable on giants in addition to humanoids.
- Web has no limit on the distance of anchor points, so it can be used outdoors and apparently anchor against Eberron's moons. Webbed creatures can't attack.
- Charm Person and Charm Monster are more powerful, in that the victims will fight hopeless odds for you. They are less flexible however, in that you can't give the target any other commands. (Command Undead and the like are similar). All classes (even non-spellcasters, as of Update 26) have a 'dismiss charm' feat that will allow them to cancel their charm. (It's not known if a character can dismiss another's charm spell.)
- Dispel Magic has many fewer applications, most of them only effective against PC's, as monsters almost never buff themselves in any significant fashion.
- Many spells have had their damage ranges altered slightly. Spells which use d6s in PnP usually use 1d3+3 in DDO, to ensure the players always deal a good amount of damage.
- Spell Resistance *only* applies to spells that produce non-damaging effects like Hold, Charm, Enervate, etc.
- Anti-magic effects produced by Beholders *dispel* all buff spells instead of simply suppressing them. Effects produced by items, however, are not affected in any way and always apply. Other anti-magical effects in the game, however (Globe of Invulnerability), merely suppress buffs instead of negating them.
- Transitioning into an adventure/quest area dispels all spells except special "lasting" effects from a number of sources (such as certain NPCs). All standard buffing must take place inside the quest/adventure area itself.
- You can only Summon one monster at a time, and you can't get rid of it until it either dies or the duration expires. Summoning a new monster will cause an existing one to vanish.
- The concepts of languages and literacy are gone.
- NPC clerics will provide free "Half-True, Half-Turbine" Resurrection, in addition to other pay per use spells. Potions can be bought to heal common ailments like Curse and Blindness.
- While it is possible to acquire negative levels, negative levels never result in actual level loss. Instead of giving a -1 penalty to saves, skills, and attacks negative levels give a -2 penalty. Thus even a relatively small number of negative levels can be severely debilitating.
- Fear effects prevent attacking, spellcasting, and skill usage, but do not affect movement.
- Characters, NPC's, and monsters don't die when they hit 0 CON, WIS or CHA. Instead, if you reach 0 in any statistic due to draining or damaging effects, you become helpless. You can move, but cannot initiate any other kind of action. Normal and elite monsters can be drained to 0 in a stat and will become helpless, but their stat totals reset after a given amount of time depending on the difficulty setting on the quest. Bosses cannot lose more than 10 points in a stat and will flash a red heart over their heads indicating they are at maximum stat drain. Raid bosses are immune to stat drain.
- Many, many monsters have immunities that they don't have in PnP. Most vulnerabilities are intact, although some are less in degree.