You won't be disappointed for one of 2009's best games.
I think alot of people remember the flop Killzone 1 was. I remember borrowing it from a friend expecting a great game. I was definitely disappointed after playing the generic FPS. When I heard Guerrilla Games were making a second I didn't really care. But now after playing it, they sure have improved in creating videogames.
Let's start with the campaign. After a short section where you walk through the main ship to your landing pod (not sure exactly what it is) you're thrown straight into the action. This is a good way of beginning action games I think. It gets you interested almost instantly and keeps you on your toes. After a few missions the pace slows down a bit to let you take a breather, but that doesn't mean it will be a walk in the park. The campaign is actually quite good. I'm not usually a fan of FPS story modes, but this one got me hooked from the start and kept me interested. Funny thing is that I did it on the easy mode, but died more than a few times.
The story itself is okay. You're the typical space marine (who isn't this generation?) sent to Helgan to attack the Helghast. Who are a very Nazi-ish race. The main difference in this game is that you're attacking their planet, and not the other way around. The story all round is not bad, and the ending is quite good. Not to spoil anything, but there is definitely going to be a Killzone 3.
I think the worst thing about the game are Rico and Natco. They are two of your three team mates through the main story. The third, Garza is the only good one of the team. These two guys make the most idiotic decisions in the game and easilly are total "meat heads" Try and look past these two idiots to enjoy the game itself.
Another thing to mention is that the controls are a bit heavy. They may feel unresponsive at first, but this is to make it feel more like you're controling an actual person with equipment rather than a balloon with a gun. You can change the sensitivity in the options menu to get a feel you like. I got mine after a minute or so of fiddling around with it.
The multiplayer is executed extremely well. There is ranks, leveling up, classes (similar to Team Fortress 2 which I also love) and clans. I played a few hours of it and loved every minute. It's fast paced, possibly faster paced than the gameplay. One unique feature is "Warzone". Which is a mode that changes the game type in the middle of the match. One minute it's "Deathmatch" the next it's "Capture the Flag" I hope more games use this in the future.
Overall, Killzone 2 is an extremely fun experience with a good campaign and an excellent multiplayer. Buy this game and enjoy one of the PS3s best games.