This is an awesome game as far as the single player goes, easily the best FPS/TPS released in the last 18 months. The graphics, gameplay, level design and attention to detail are all top notch and the story is pretty good too. I very highly recommend it. This is the one and only game where the graphical quality benefits a lot from SM3 and HDR, but the 1.4 patch enables a pseudo HDR mode for ATI X800 cards. Get that before starting to play.
Note that unlike the previous games, you can interrogate every enemy guy in the game, and the game actually rewards you for not killing them. Some of them say some pretty hilarious things too.

The co-op mode on the PC version is totally messed up, however. It's essentially dysfunctional in its current state. Don't expect to get anything out of that, although TVT mode works okay. Also, this game does not work on XP 64-bit due to the copy protection. Of course, it's easy enough to get around that, but something you should be aware of if you run that OS.