The PC version is (thus far) absolutely fantastic. The game engine is ridiculously well optimized (I'm running the game at 1680x1050 on Very High with hardly any slowdown at all, while the first Crysis would barely average 20fps at those settings). The controls are very fluid, the artistic design is great and the level design is intuitive yet encourages some exploration.
If there's any real criticism I can throw at the game, it's that it's a pretty significant departure from the original Crysis (at least so far), and that's fairly disappointing. The first game had massive, sprawling environments and gameplay mechanics that truly let you play the game how you wanted. Hell, one of my best experiences in gaming happened in the third level of that game, where I ran out of rocket launcher ammo and had a helicopter in pursuit. I was forced to make my way downstream without any means of shaking off the helicopter, so it was a tense game of cat and mouse for over an HOUR before I found an RPG and shot the bastard down.
Like I said though, Crysis 2 is fantastic so far and I can't wait to play more. It's just a shame they took away some of what made the original great.