Crysis 2 is a confused game because I'm not sure it knows what type of game it ultimately wants to be. It plays like a FPS, but it succeeds more when it's played as a stealth game à la Metal Gear Solid. Granted, you have a nano suit that gives you augmented abilities like increased strength and armor. But those abilities are almost rendered moot considering you can often avoid combat all together with the cloaking ability that makes you invisible for a brief period of time (but which you can increase the duration later on with an upgrade).
And it's often better to avoid combat in the early stages to bypass frustration, as eliminating enemies just leads to more enemies spawning in an endless cycle. What's even more frustrating is these enemies have a nasty tendency to spawn in areas which you have previously cleared making any backtracking a risky proposition that can lead to (many) unexpected deaths.
The game has a sizeable campaign for a FPS. I clocked in just under ten hours (at 9:59:43) on "Normal" difficulty. I imagine on the hardest difficulty, as well taking the time to find all the hidden collectibles in each level, you can easily bump that figure up several more hours. Nevertheless, the game ends up feeling twice as long depending on how many times you die and have to replay certain sections. The story is pretty forgettable consisting of an alien invasion on one hand and soldiers from a private company who are after you--or more specifically--your nano suit. Unfortunately the story didn't really engage me despite me earnestly trying to get interested, but I just couldn't. So the majority of the time I had no idea why I was doing the things I was, and I simply fell into the rote process of shoot baddies, move on to next checkpoint, roll credits.
I guess that says something about the mechanics of the game, as I was completely lost plot-wise but physically playing the game was somewhat enjoyable. Once I figured out how the game "plays" I got in a comfortable groove. You really have to utilize all your abilities to survive as you won't last long in a straight-up firefight. Enemies are ruthless and accurate and will come searching for you if you make yourself known to them. You often find yourself employing a lot of guerilla warfare-like tactics by cloaking to flank enemies, shooting, re-cloaking and then running off to another position to catch them off-guard again. Your suit does have armor but it becomes virtually useless when fighting against multiple enemies which is why it's best to stick to the cloaking ability. Another advantage to being cloaked is your ability to silently take down enemies reducing the risk of setting off an alarm. Plus it's morbidly satisfying to run up behind an enemy and shove a knife in their chest while they are completely unaware.
The game is nothing spectacular while at the same time not a complete waste of time. I did run into one glitch towards the end. You need to defeat four specific aliens in order to unlock a huge gate to access the "mothership" to destroy it. Each time you kill an alien it unlocks the door by 25%. However, the glitch happened where after successfully killing three aliens (75% unlocked) the fourth alien would NOT appear anywhere even though I could hear him apparently running around, but he never appeared on my screen or came after me which led me to running around aimlessly trying to figure out what was wrong until I just killed myself and restarted that particular section.
Having never played the first game this was my introduction to this series. I found that I wasn't blown away, nor was I turned off. The game seems to rest in some sort of purgatory for me as far as overall feelings towards it. The only overwhelming positive thing I have to say about Crysis 2 is the soundtrack is excellent (not surprising since Hans Zimmer is at the helm), and during the course of normal play you unlock what appears to be the soundtrack in its entirety. This was a rental for me with no preconceived notions about what to expect. I enjoyed it for what it was worth. My suggestion to anyone on the fence about this game is to do the same.