PnP differences

 Adventuring 


 * The concepts of darkvision, low-light vision, and portable light sources are gone. However, areas do have varying amounts of light which affects the difficulty of hiding.
 * Throughout the dungeons are scattered "rest shrines", which enable you to heal hit points and spell points. Most rest shrines are adjacent to resurrection shrines, which can raise you if you die.
 * The number of monsters you will encounter is significantly higher. It is easily possible to encounter several dozen monsters over the course of one mission, and some missions have over a hundred monsters. The daily spells alloted to a caster have increased proportionately.
 * The penalty for dying is significantly lower. While in PnP you lose a full level if you die, in DDO you lose only approximately 1-2% of a level.
 * The rate of advancement is significantly lower. While in PnP you advance a level after every 13-14 encounters, in DDO you will probably have way more than that many per quest, and each quest might only give you about 5-15% of the experience necessary to advance a level.
 * No way to damage another PC (except with rare bugs). You can detonate a Fireball on your team and yourself with no risk.  Occasional spells can impair other PCs, like Grease or any AoE blindness.
 * Portcullises, although see-through, are impervious to spells, arrows, and greased halflings.
 * The typical dungeon trap is a magic energy shooter which operates continuously once triggered, rather than a one-shot danger.
 * DDO dungeons frequently feature gates and chests which can only be opened when some certain monster dies (or set of monsters). This can be particularly annonying if you Charm the monster, and no longer can attack it.
 * There is no movement penalty for being a dwarf or wearing heavy armor.

 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 recieve +20 hp at first level, and full hit-dice thereafter. (This makes a high constitution relatively less valuable)
 * Sorcerors can never unlearn a spell as they advance.
 * Clerics have no domain or identified deity.
 * Wizards have no familiar or specialization.
 * Wizards get bonus metamagic feats at 1st, 5th, and 10th level.
 * Rogues get sneak attack bonus on any enemy not attacking them, regardless of awareness. They also can Hide without cover.
 * 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 +2 on AC and saves to all allies within its radius of effect.
 * Multiclass characters never have an XP penalty.
 * The druid and monk classes have been removed from the game, and there are no prestige classes.
 * Characters can reach a maximum of level 10. (This level cap may be increased in later updates.)
 * Enhancements provide a new method of character advancement.

 Races 


 * Warforged have almost all their immunities turned into +3 on saving throws. At higher levels they can spend feats or enhancements to get the immunities back.
 * Paladin Lay on Hands produces Divine Cure or Repair, as appropriate.
 * Halflings have lost their penalties of slower running speed and smaller weapon sizes. Their advantage of fitting in smaller spaces is also gone.
 * Female dwarves cannot have mustaches.

 Combat 


 * Combat is real-time, not turn-based.
 * The concept of attacks of opportunity, grappling, initiative, and being flat-footed are 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 AC and Reflex saves.)
 * PCs receive a second attack at BAB +1, instead of BAB +6. (This makes feats which grant a second attack, such as Cleave and Two-Weapon Fighting, relatively less valuable)
 * Nobody can be disarmed. Sunder debuffs AC instead of breaking equipment.  (This would make monks relatively less valuable, if they were included at all)
 * Regardless of your Swim skill, underwater combat is impossible.
 * It is possible to "block" by holding Shift. While blocking, you may not attack, but you gain a +2 bonus to AC and, if you have a shield equipped, you gain some DR.
 * Shields are more powerful, as they provide DR when blocking (see above). Thus, weapons which disallow shields (i.e., 2-handed weapons and two-weapon fighting) are relatively more risky.
 * Drawing a dagger into your off-hand takes much longer than equipping a two-handed weapon or tower shield- essentially, too long to be done in combat.
 * Melee (not ranged) attacks have a -4 hit penalty while moving. The feat Spring Attack negates the penalty.
 * Characters suffer a -4 hit penalty when moving during combat. This effect is negated by tumbling.
 * Repeating crossbows fire three shots at a rate of fire faster than a bow before requiring a reload.
 * Heavy and light crossbows reload at the same speed.
 * Darts and shurikens cannot be thrown from both hands.

 Monsters 


 * Touching a Black Pudding or other ooze monster does not hurt you, so you may attack with Unarmed Strikes without worry. (That will be the most affordable way to kill them)
 * Monsters' regeneration (such as on trolls) 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.

 Equipment 


 * Magic items have a minimum character level prerequisite to equip them. The limit seems to be (Plusses*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/sorceror1 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, Rangers (and Rangers only) get a class feature that allows them to add their Strength bonus to bow damage.
 * All weapons have just one physical damage type. Daggers can't Slash, and Morning Stars can't Pierce.
 * Coins are weightless and take up no space, while gems are low-weight and occupy nearly as much volume as platemail armor.
 * 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.
 * Although Silver, Cold Iron, and Byeshk weapons exist in the game, there are (at present) no monsters against which they are useful.

 Feats 


 * 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. (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). Certain enhancements can increase the AC bonus, but they also increase the attack penalty.
 * 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.
 * Cleave has been changed to be an active feat that allows you to attack enemies in an arc.
 * Several new feats have been added, such as Precision and Slicing Blow. However, many of them do not appear to be very useful.

 Skills 


 * Skills gone: Knowledge, Climb, Sense Motive, Disguise, Spellcraft, Craft, Escape Artist, Sleight of Hands, Rope Use.
 * The Intimidate skill is used in combat to draw the attention of an enemy.
 * The Diplomacy skill works the other way around (enemies targeting you will switch their focus to somone 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.
 * 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 


 * Spell points from different classes (e.g. wizard, sorceror, cleric) stack into one common pool.
 * 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.
 * 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 use the same material component (if they have an MC at all). Stoneskin is currently the only exception, and has its own expensive component as usual.
 * 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)
 * Touch spells now have a range over 15 feet. This applies equally to helpful (Cure Light Wounds) and harmful (Shocking Grasp), making all Touch spells more powerful.
 * 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, Fly, Dimension Door, Teleport, Spider-Climb, Knock, Polymorph, and almost all Diviniation 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.
 * Flame Arrow- only allows arrows, not bolts, axes, or daggers.
 * Web has no limit on the distance of anchor points, so it can be used outdoors and will anchor against the moon. Webbed creatures can't attack.
 * Charm Person and Charm Monster are more powerful, in that the victims will fight hopeless odds for you. But they are less flexible, in that you can't give the target any other commands, and also can't end the spell early (Command Undead and the like are similar)
 * Dispel Magic has many fewer applications.
 * Many spells have had their damage ranges altered slightly.

 Miscellaneous 


 * The concepts of languages and literacy are gone.
 * There are no NPC casters who will cast spells for a fee. NPC clerics will provide free Raise Dead, but not any other service.  Potions can be bought to heal common ailments like Bestow_curse and Blindness.
 * While it is possible to acquire negative levels, negative levels never result in actual level loss.
 * Fear effects prevent attacking, spellcasting, and skill usage, but does not affect movement.