From what I can tell is the enjoyment level of this game is directly related to the Graphics settings you run.
Not really sure why that is, but it really effects how you view the game.
When you get to the point where you run the game at MAXIMUM Settings. hehe. The game is amazing, I found myself in some parts almost unable to distinguish from real life (looks - not crazy I'm going to shoot people) With lower graphics settings, and lower resolutions I played the same couple of areas and the game Did NOT feel the same at all. lost a lot of it soul!
I do run SLI GTX's, and at times still feel that it is to slow, But I just can’t wait for the day I can run this game at my 1920X1200 @ 8XAA w/Super Sample / 16AF at 45FPS Minimum 80 Average.
I average 36 now with my SLI GTX's at all ultra like settings, w/ 28FPS minimum.
I suppose SLI 9800GTX's may get me close, but I thinking more then likely SLI 10800GTX's, will get me there.