I think there are lot of features/small details that are very unique and shows the love that the devs have put into the game.
For example players are encouraged to dive after another player if he falls of the roof, now how cool and unique is that.
I dont think any other games has something like that. You take a scene from the movie and turn it into a gameplay element, awesome.
And small things, like when you aim you get those small black bars to up and down to you view, for the movie-effect, that is also
very nice touch.
And the animation when you do the slide and turn backwards, so the players is shooting in his back, again never before seen in any game.
And looks awesome.