GTA3 as some non-reality, at the expense of a crappy story.
You don't care at all about what will happen next. I wouldn't call Mafia "non-linear" since you end up having to followi the story.
Deux Ex is a good exemple since you can change it based on your action.
What would be better would be the non-linearity of Deus Ex's story with the freedom of GTA3...
That said, Unreal2 seems like a great game and why would you bitch because a game as gone gold?