I haven't been able to play Crysis 2 much, but the things I did see were pretty damn good.
Also, I am a huge MoH fanboy, so this decision might not be the most biased on my part xD
MoH is great, but short, Crysis 2 is a beast but requires powerful hardware. If you're looking for something to really sink your teeth into, Crysis 2. If you want to just "waste" (in a good way) a few hours, MoH.
If you played any older MoH games, however, be prepared for big changes, and not just because of the modern warfare setting. This is the first game (after Allied Assault; Airborne had nothing of it) that actually puts you in a storyline where you as a player can truly connect to your character, as well as experience some powerful bonds with other characters in the game. Think of "Brothers in Arms". Having said that, and without wanting to spoil the ending, it might not be what you expected. On my part, it was kind of... well, sad and also disappointing just a bit; but still a great ending.