Crysis Warhead is a stand-alone expansion to Crysis. It doesn't require the original to be installed, or even have been played, but it certainly does help. Crysis Warhead is, in my opinion, a better game than Crysis. It has more persistent and ongoing narrative chatter, making it feel like an enormous, open-world style Soldier of Fortune game.
Except, it has heaps and heaps of technology, just like the first game - modify your suit's mode to the scenario, modify your weapon to the scenario - and smash to bits the enemies along the way.
There's more emphasis on vehicles than in the first game, and while it tries to do some "on-rails" vehicle combat early in the game, it is still not quite on par with the on-rails segments in games like Gears of War. Granted, these aren't entirely scripted scenes, and while Crysis Warhead gives you the impression of being a massive open world, I'm relieved that the game is somewhat linear.
Open world games tend to dilute their stories in exchange for giving the player lots to do - this in turn leads to a scenario where the mechanics are repetitive, and the only thing that is different is the terrain, and the people telling you what to do.
Crysis Warhead escapes that by having some sort of story to string you along and keep you interested. Graphically, its very impressive, just as the original title was. It isn't however, something that you'll play for years and years to come - as it does devolve into being a fairly generic shooter after you get over the initial hocus-pocus that any game labelled with Crysis tends to have.
It runs pretty well on modern operating systems, which is an important thing for a game of its age - but for me it did not seem to support widescreen modes correctly out of the box, and I couldn't really be bothered fixing it - so I played in 4:3, as demonstrated in the screenshots I took while playing. In 4:3 the game feels dated, owing to the lack of a broader field of view.
It exhibits the same AI problems as the first Crysis title, with enemies tending "stalk and stack" along their way to finding you along what seems to be pre-defeined paths. Of the AI, I have one thing to say:
Of the game itself - it's pretty good.