I've yet to play through Crysis 1, but we got to start from somewhere, right? The graphics are slightly worse than Crysis 2 and the enemies seem to have binoculars for eyes, and there's no multiplayer or expansion pack (Warhead). But it's still a pretty decent game.
Crysis 2 is better in my opinion. The graphics are much better (to me, at least), and the addition of upgrades to your Nanosuit make it the better game. Oh, and it has decent multiplayer, whereas Crysis 1 has NO multiplayer.
But don't forget about Crysis 3. The campaign's much shorter than Crysis 2 (Crysis 2 has 19 missions, while Crysis 3 only has 7), and there have been a few reports of glitches (I had the game freeze a few times), but the multiplayer more than makes up for it.