Peter Molyneux said something really interesting during one of the panel sessions he was at. I can't find my notes at the moment, but the gist of what he was saying was this: One of the more important things a game can do for a player is allow them to learn more about themselves by playing the game. In essence, the game could facilitate your journey of self discovery. So his intent when you play his games is you might get through them and find yourself saying "huh, I never realized that about myself." I think you see a lot of this philosophy in the designs of fable and black and white, where the world reacts to your actions, and it sounds like fable 2 is going to take it even farther.
I think you could arguably see something similar in The Sims. Playing The Sims taught me all sorts of things about myself. For instance, apparently I'm the sort of person that likes to trap people in burning buildings. Er, I mean..
While I mock, I really do like this idea of games as self exploration. We have the unique ability to put the player in situations they'd never be in otherwise, and the player can learn a lot about themselves by how they react while still in the safe confines of a game.
I think as a bit of self-assigned homework I'm going to look at various games and try to figure out how they could be redesigned to be magical journies of self discovery.