This is basically speaking the best FPS game there is.
Gameplay and opponent AI are really good keep shooting someone and then cloaking the enemy will eventually start shoot blind or lobbing granades at you.
Sound is amazing. I've actually heard an enemy approach due to them stepping on a twig (or some sort of noisy surface)
I
'm rating this as a single player game as I haven't gotten into the multiplayer side of things yet. (due to the brilliant storyline)
Longevity shouldn't be a problem due to the multiplayer but still to be verified.
One word of warning, If you're not sure if your PC/Graphic Card can handle Crysis, then it probably can't.