Certain subraces are considered to be more powerful than other races, typically because they feature ability bonuses with little or no penalties. These races are given a level adjustment that modifies the amount of experience the character must gain in order to increase in character level.
A character with a level adjustment requires more XP to reach a particular level. The additional experienced required is commensurate with the level adjustment of the subrace in question. Characters with level adjustments will always be one (1) to three (3) levels behind characters with the same amount of experience that do not have level adjustments.
For example, a drow elf has a level adjustment of +2. The character will be only level 3 when his human companions are level 5. Similarly a deep gnome, with a level adjustment of +3, would still be first level while his halfling companion is level 4.
A character with a level adjustment can reach the level cap of 20 provided the campaign or module supplies enough XP. In the official campaign, a character with a +1 level adjustment will usually have this happen during the large battle at the keep. With a character with a +2 level adjustment this usually happens close to the final battle. However, characters with an adjustment of +3 will most likely not be able to obtain the level cap of 20 by the end of the official campaign unless they employ "milking" strategies to obtain additional experience points, either from re-spawning monster areas or spell-like abilities.
It should be noted that in NWN2, ECL only affects the experience needed a given level. It does not affect the 'effective level' or 'challenge rating' of a PC. While this means that a level 15 drow fighting solo will earn the same XP for killing a dragon as a solo level 15 human would, it is important to remember it takes the drow considerably longer to gain the (additional) experience necessary to advance to level 15.
Equally crucial to understand is this: the party's average character level is used to determine earned Experience for an encounter, not ECL. This has a profound impact on high ECL races, as they will cause the party to earn accelerated experience points during play because they bring the party average level down.
3.5 Rules ComparisonEdit
Subraces that can be used as player characters have a level adjustment, which is a number that is added to the creature's total hit dice to arrive at its effective character level (ECL). A creature with multiple special abilities is more powerful as a player character than its hit dice alone would indicate. For example, a drow elf has spell resistance, bonuses to its ability scores, and spell-like abilities. Its level adjustment of +2 indicates that a 1st-level drow wizard is the equivalent of a 3rd-level character.
Level adjustment is not the same thing as an adjustment to a creature's challenge rating because of some special qualities it possesses. Challenge rating reflects how difficult an opponent is to fight in a limited number of encounters. Level adjustment shows how powerful a creature is as a player character. For instance, a drow receives a +1 adjustment to its challenge rating to account for its special abilities, indicating that it's tougher in a fight than its hit dice would suggest, but its level adjustment is +2 to balance its abilities over long-term play.