Hop over there and you'll find 'A Very Crytek Christmas' on the front page, the game mixing scrolling rhythm play with a couple of Xmas classics. The Crysis developer says it's giving the money it would normally spend on Xmas cards to charity, instead choosing to spread some holiday love this way.
Not that the game itself is particularly charitable. You can either try Silent Night on normal difficulty, which is tricky enough on its own, or you can get your butt rhythmically kicked by the expert-rated Jingle Bells. At least you'll have a few familiar Crysis faces to festively cheer you on, or in our case tell us we're hurting their ears.