Well the game itself is quite fine as a game, but as a sequel to Crysis it's a let down. It's basically an extremely generic shooter now as opposed to the large fun environments of Crysis.
Just to clarify some of the larger problems:
For single player:
1. AI is mediocre, sometimes they are extremely stupid, sometimes they spot you through a wall half a mile away.
2. Nano Catalyst is bugged, there have been a number of people who upon exitting the game have had their Nano catalyst reset, I'm one of those people, it makes trying to save for the upgrades impossible and basically breaks one of the main features of the game.
3. The campaign is completely mindless, you might as well have unlimited ammo given how frequent ammo caches are, there's no reason not to use armour mode to blast everyone down and then just restock ammo. Stealth mode is also not as well done as in Crysis 1. You can sprint around in stealth mode and not care be spotted, sometimes aliens jump at you from 10 meters away even if you are sitting still in a dark corner with stealth mode, sometimes you sprint past them with no detection.
1. Server finding is tedious, the server list updates extremely slowly, adding to favourites is overly complicated. Many servers don't even respond half the time.
2. Product key problem, this affects many players who bought over steam and probably a few who bought in stores, there is a problem with the product key not working for MP claiming that it's already in use. There is also the problem of the key having to be entered every time you open the game because it doesn't save. There is now a workaround for it but it still reflects very poorly on the development of the game.
3. Servers refusing to start, the servers freeze at 1 in the countdown, this requires manual restarting of the server.
4. No joining active games, despite it not mentioning it anywhere in the waiting lobby, sometimes you are stuck there simply because the game is still going, you have to wait until the next round before you are able to join in. This I feel is a terrible system for a PC game that contains a server list. But in true console port fashion the quick match works, but it puts me on a server in the Netherlands, I guess at least I got a game started.
5. The multiplayer itself is fun, but not as fun as the original Crysis multiplayer and just feels like CoD with less weapon choices.
Overall the launch of Crysis 2 reminds me of the launch of Spore, it's a reasonable game in its own right. But completely fails expectations and was utterly unable to achieve its full potential. For a game that isn't exactly in line to be the next big FPS king such a terrible range of issues could severely shorten its lifespan.