Multiclass enhancements

One of the biggest character-design features that separates DDO from PnP D&D is the four "enhancements" slots every character recieves, and which can be changed four times per level, as you gain XP. PnP has nothing even remotely similar.

The enhancements you are allowed to select are determined either by your race and character (total) level, or by your levels in a particular class. A halfling rogue4/ranger3 could pick enhancements from rogue 4, ranger 3, or halfing 7.

The enhancements give substantial extra power. At low levels, each enhancement is almost as good as 1 normal feat, and they rapidly improve as you advance. By 10th level, one enhancement can be worth 3 or even 4 feats. (To compare the value of a feat versus an enhancement, look at the Weapon Focus Thrown feat versus the Halfling Thrown Weapon Attack enhancement series).

Some of the best enhancements are the ability score improvements, which will eventually give you a +3 to the primary trait of their class (except for barbarians, who get the bonus in consitution instead of strength). Nonhumans also get a boost in one of their race's advantaged ability scores, which makes it additionally important to choose a race matching your class. (Humans, instead, get a lower bonus to any ability score). Those bonuses are separate from the usual ability improvements at 4th and 8th level.

Also quite important are the percentile spell-boosts, which can provide 40% more effect from a low-level healing or fire spell- almost like Empowering all such spells, with no additional spellpoint cost! (Meaning that when you first learn Fireball, it will do less damage than your previous Burning Hands) The existence of such great enhancements means that a character without them is at a large disadvantage.

Class enhancements are usually better than racial enhancements. For comparison, a level 8 Halfling gets +2 dexerity, but a level 8 rogue gets +3 dexerity.

The consequence of the above rules is that multiclassed characters cannot get the same quality of enhancements as a single-class character. They have the access to the full assortment of racial enhancements according to their total levels, but those aren't as good as class enhancements. They also have access to class enhancements from each of their many classes, but still can take only four total.

A level 5 wizard will have 4 enhancements, one for higher intelligence, one for more spellpoints, and two to boost his favorite kinds of spells. A level 5 fighter will use 4 enhancements to improve his battle power. But a maxxed-out wizard5/fighter5 still only has 4 enhancement slots, not 8. Unless all the enhancements are from the wizard list, then he will be worse at magic than a pure wizard 5. And if he does that, then he'll have no fighter enhancements, and be worse in combat than a pure fighter 5.

Therefore, in exchange for removing an XP penalty that was never particularly importance (given racially favored classes), DDO has made multiclass characters even weaker at class-abilities than a singleclass character with the same class levels and lower total levels. The only way multiclass characters could be competitive is if they where allowed to learn more enhancements than others (prehaps 6 instead of just 4)

In summary, before you create a multiclass character, carefully read over the enhancement tables to decide what you'd like to take. If you go with a 5/5 or 6/4 level split, then your only high-level enhancements will be the racial ones (which are not as good). A 8/2 or 9/1 split will enable you to take focus on the enhancements from your highest class, while still having some unenhanced abilities from the secondary study. (It seems that level 8 is an important plateu to hit, because that's where you get the +3 ability score)