I'll give it a shot!
* the freedom to decide to be good or evel (with an consequence in the end [what makes it worth to play it again])
This reminds me of another old favorite of mine: bioforge.
http://en.wikipedia.org/wiki/BioforgeWhile it was not an FPS, the concept that you did not know who you were, could discover that as you played the game and that choices you made in the game determined who you were ... that was just cool! And, yes, it made you want to play again to try and determine a different outcome.
