Killzone 2 has a great multiplayer but the single player campaign isnt the best
The story isnt interesting and perhaps you will do it once or twice for the trophies. I think they had to take a little more time in that area.
Now, the multiplayer. The main reason I bought this game was for it and Im not disappointed so far. You can play with 36 players online and do alot of activities like the most deaths, capture an object and put it in the enemy base, assasination and other stuff.
You can be a Isa or Helghast but sadly (for what I have seen), the Isa tends to win almost always. You also can choose different classes and even, skill from other classes. Another thing that I can say is that you level up and can earn badges.
The most important feauture of Killzone 2 are the graphics, those graphics are great and one of the best you will ever see.
Killzone 2 isnt the best first person shotter, yeah, it is great and all that but as I said, it has its flaws. The control isnt the best but at least you can play. If you are looking for a great multiplayer experience then you should get this. If you want it only for singlepayer then better rent it.