In the original Crysis, you fought off North Koreans, discovered an extra-terrestrial plot, and began the fight for humanity, all as the special-ops agent codenamed Nomad. But as you saved the day in the main storyline, your cohort Psycho was off on his own mission. Warhead shows you what he was up to, by putting you in his head and unleashing you against the dastardly enemies who stand in your nanosuit-powered way.
Crysis is an open-ended first-person shooter in which how you proceed is really up to you. Set on a beautiful tropical island filled with lush scenery, flora and fauna, you're equipped with a special nanosuit that allows you to cloak, speed up, increase your strength, or increase your defence. This nanosuit affords you a number of options in how you want to take on your enemies: do you sneak up behind them, grab hold of your target, and toss them into their ally? Or do you stay in the underbrush from a mile away and pick off your targets with a rifle? Of course, you can always just run into battle, guns-a-blazing, if that's your thing. Or punch everything with super strength, sending it skidding across the ground. The possibilities are endless, and it leads to replay certain encounters again and again, just to see the different results.
Warhead doesn't really deviate too much from this formula, but that's alright, because it doesn't need to. Some level design does change, though. Levels are fairly smaller in this expansion, but with more in them. In the original, while you spent most of your time walking through long, lush, but boring valleys, this one had the action more condensed. The pacing is much improved (except for one prolonged cutscene somewhere near the end of the middle), leading to less running around and more shooting/punching/tossing/humiliating your foes. Overall the game can last about six to seven hours, depending on your play style, so while it not be a lengthy campaign, it's a good addendum to the original's plot.
Additionally, as opposed to the sudden appearance of aliens doesn't suddenly eliminate the Korean presence on the island like it did in the first game. Both groups will show up as your aggressors throughout the game, sometimes at the same time. This leads to you being able to get them to combat each other, letting you either slink away in the firefight or simply eliminate the last remaining forces.
Crytek have also stated that the graphics have been optimized, and therefore aren't as system-taxing as the original Crysis. While I've heard some reports to verify this, I've also heard that there are some problems with how the game goes about its graphical business. While I didn't directly notice these problems with the exception of an odd framerate hiccup, reports of unreasonable slowdown and graphical glitches are somewhat common.
While Crysis: Warhead doesn't really bring anything new to the series gameplay-wise, the expanded-upon storyline and better pacing of the game will intrigue any that enjoyed the original Crysis. Wide open settings, fast-paced action, and the ability to fling someone across a great distance make it a fun game to play, especially with all the different ways to approach a situation. So, while it may not be everyone's cup of tea, if you enjoy a bit of choice with your explosions, and enjoyed the original, Warhead is definitely the game for you.