I skipped this when it was released, but picked it up during the Steam Holiday sales.
I'm going to be a bit biased towards it because it's been a long time since I have played a straight up shooter, and it was quite refreshing. It actually has me contemplating a purchase of Homefront at full price, which is something I try to avoid anymore for most games. (Steam sales have changed my purchasing habits.)
If you haven't played the original Crysis, you will have no clue what the hell is going on in the story. Despite this being a standalone product, they explain nothing and expect you to know what's going on. I cannot stress this enough. I started off not knowing the mission or even remembering how to work the suit because there's not even a tutorial mission.
You play as Psycho, a British operative, who was around during the original game, but was running a different mission than that game's central character, Nomad. Same area though, so Psycho is facing the same enemies, North Koreans and aliens. Your mission is to chase down General Lee (I'm not making this up) and recover whatever it is he's trying to protect and take back home.
You're helped by some chick's voice at HQ, and a pilot named O'Neill. The O'Neill relationship is odd, and poorly explained through black screen (for me, maybe there was video?) events. You'll hear audio, but see nothing. The audio doesn't really explain anything except that O'Neill goofed up during training and Psycho washed him out. Not well written or executed to say the least. You also will fight alongside a few other guys wearing the same suit you have on, which really dilutes the concept behind the story and makes you wonder why you're so special.
I mean, shouldn't there only be a few of these suits? That was the whole point of the original storyline, which this parallels. Now other Americans are running around in them, and the Koreans have them. WTF?
Anyway, game play is exactly like the original. It's an FPS and your suit is the star by allowing you to run faster, jump higher, punch harder, shoot straighter, cloak yourself, etc. Only one of these functions can be used at a time (in Crysis 2, you can reportedly active two at a time), and you have limited energy, which does replenish quickly, but don't expect to run through the game cloaked.
The aliens are the same as in the original, but they seem to have been slowed down a bit, and weakened. One of the biggest complaints about the original game was how ridiculously fast and durable the aliens were. Fast was an even bigger problem when they were flying. And I should point out that I'm referring more to the grunts than the bigger ones.
There are a couple of cool, and bad, "mini-scenes" that occur during the game that essentially changes the gameplay. For example, there's one area where you're racing a hovercraft while aliens snipe at you.In another, you're defending a point with some other U.S. troops against waves of aliens.
Overall, if you're into the Crysis universe, this is worth a playthrough. Although, I think I'd hold out until it hits $5 on Steam.
If you're not into Crysis, you should go give Crysis a try, but save this until you know if you like Crysis or not.