I think both are good but Crysis 2 is better. It has a darker and more serious tone, more realistic and immersive, Alcatraz wasn't a cocky smartass like Nomad, and there's no bull-blam!-, like certain enemies getting a ridiculous damage boost to cover up for their stupid AI, and an unnessacary boss battle that was so ridiculous and unrealistic it was excruciating. Also in Crysis 2 you dont walk ludicrously slow, and the weapon sandbox is bigger. Plus I like Crysis 2's story better.
But Crysis had some things over Crysis 2, like carrying 3 weapons, dual wielding and able to carry more heavy weapons and grenades. And there was an alien weapon. There was also an animation for picking up weapons and ammo. Plus the whole game was more open and at some parts you have to be mor tactical than you ever did in Crysis 2.
And I'm waiting for Crysis 3 to come out before judging it
[Edited on 12.29.2012 7:42 AM PST]