As with the first game, Crysis Warhead's storyline involves you with fighting the North Koreans who in this game are trying to gain possession of an alien artifact and get it off the island. Later you deal mostly with an alien threat who have been on the island for a long time and are now waking up and freezing the tropical environment in an apparent attempt to take over the world.

Crysis didn't really deal much with how your character evolves in the course of the game; you were basically just a guy who killed things. Crysis Warhead is actually a deeper game in terms of trying to make Sykes more than just a run-and-gun shooter. He has a friendly relationship with another character, a drop-ship pilot named O'Neil. As you play through the game you learn that O'Neil was training years before the game's event to join the nano-suit wearing special forces group alongside Sykes but basically washed out. This buddy cop set-up in Crysis Warhead gives the game a little extra heft it might not have otherwise.
Of course, all this stuff about character and motivation might make you think Crysis Warhead was getting all super-deep and complex. It isn't. In fact, the game is much more linear that the original title. There are some levels where you can go in different routes to get to your objectives but Crysis Warhead's single-player experiences is clearly made to be more focused on you getting from point A to B and blowing up a lot of stuff along the way. Indeed, there is a "rail shooter" sequence that is more literal than you would believe.

There's actually little that is really "new" in the single-player game. There are few new weapons to play with like some mines that you throw down and are designed to detonate when a vehicle runs over them as well as a new grenade launcher. AI in the game is basically the same as in the original Crysis and that means it's better than most. There's been an attempt to improve the hovering alien's AI performance this time around but it's basically the same kind of behavior that the original game had; they tend to still charge and leap at you for the most part but they have also learned a couple of new defensive tricks that we won't spoil here.