Although a game engine may not be able to really take advantage of revealing the motivations of the antagonist, it may be used to create a motivational state for the player. If the antagonist is a jerk, then the player will have no issues putting him down. When the antagonist is someone who is trying to achieve a reasonable goal using morally questionable methods, the player can't necessarily view their actions as good or evil. If the designers can make the player sympathize with the antagonist, then branched conversations, a la KotoR, Fable or Neverwinter Nghts, can be tailored to give the PLAYER the choice between doing what they know they must do (stop the antagonist) and possibly doing what they WANT to do (not be so hard on a sympathetic antagonist).