I regret to say that after playing this game I wanted to go play COD4. I don't know if this is a bad thing but I do know that once I finished the game there was, well nothing much left to do. The storyline provides a thrilling, action packed experience. With many different weapons to choose from and walls to shoot apart. But I found myself in a state of repetitiveness; about half way through the game I noticed that there really wasn't much new or exciting about this game at all. Maybe because I expected much more from it.
Sure there are some boss battles that provide an extra thrill every once and a while and the occasional turret mounting and explosive barrels exploding, but I found I was doing the same thing pretty much all the time, duck pop up and shoot, duck pop up shoot another guy and repeat. The cover system was useless for me; I'd say I used it around 5 times throughout the whole game and usually by accident. It just caused frustration and glitching.
I tried the online component of Killzone 2 and I wasn't impressed one bit, I actually have to say that I enjoyed the skirmish mode better. This is because it's more intense and the Ai friendlies actually do something because it looked like they're more engaged in the battles.
I also have to say I was disappointed that there was no offline co-op campaign. I bought this game and went over to a friend's house; we were both hyping to play it together only to find out that there was no co-op. Very, very disappointing.
But overall I think this is an average FPS and I've definitely seen better on the Playstation 3.