The first Crysis is infinitely better.
Crysis 2 is a medicore CoD clone with a rubbish story and a stealth mode which lets you sneak past everything. Boss fights suck and so do vehicle sections. It's very linear and guns feel plasticky and fake. Characters are boring and the game drags on far too long for me to actually care. The aliens are annoying and boring.
Crysis 1 is probably the best shooter that's ever been made. Directed sandbox, insane physics engine, stronger, aliens who are actually powerful and a great narrative structure. Also loads of diverse, unique missions and an amazing full out war sequence in the second third of the game makes this amazing.