Eased system reqs make gameplay superior
If you're like me, you want to see the best visuals possible. Crysis is clearly (as of right now) the most graphically intensive game ever. Crysis Warhead follows in it's footsteps, but makes those visuals more accessible. Running at roughly the same frame rate on my pc, I can run Warhead at a higher resolution (about 70% more pixels) than the original. This, in my opinion, improves the gameplay. With the added pixels, there's less blur, and you become more immersed in the jungle around you.
Warhead also benefits from a superior main character. Pyscho is far more interesting and dynamic than Nomad in the original. His dialogue is grittier (meaning he drops the f-bomb a few times a level) which feels more natural for someone in his positiion. Also, Warhead's "more aggressive" protagonist feels more likely for a dude in a crazy super-human suit. I actually found myself sneaking up on guys so that I could physically beat them, rather than shoot from a distance.
When on harder difficulty levels (Delta basically), Warhead forces you to play roughly the same way as the original. That being, sneaking around in stealth mode, popping out of cloak and eliminating a couple guys, then cloaking again when his friends come looking. This seems to be the only consistent way to have success in the game. So if you like that (like I do), then you'll really enjoy the game. Every now and then however, there'll be enemies behind you when you pop out of cloak that you missed because the jungle's so dense, and then you have to shoot your way out. Throwing the wrench in the plan you've laid out is always a fun surprise (assuming you survive).
If your computer can't quite handle Crysis, and you weren't ready to spend money on a game you were reasonably certain your PC can't handle, Warhead may be your solution. With a lower price tag and eased system requirements, it's a fun game that shooter fans will find appetizing.