Do you mean Crysis Warhead? I haven't heard of a Crysis Warzone (There's also the multi-player thing, Crysis Wars... it's confusing, I know.)
But anyway... Crysis Warhead, IMO, is a decent expansion... but like most expansions, it's "more of the same." It doesn't really offer anything "new" gameplay-wise that the original Crysis didn't have, aside from a couple new weapons and vehicles (but since you haven't played the original, that's not much of a problem.) Also, I was a little disappointed that Psycho didn't get more good lines, since he was sort of a wise-cracker in the original game (though I liked his "I'm British, you muppet!" lines.)
It's good to see that more people here are talking about FPS games...