What Killzone should have been.
Guerilla makes sure you'll never have the same experience twice because they throw in different environments and enemies to create an enjoyable experience. The AI is outstanding and you'll have to work to kill your enemy instead of always charging guns a blazing.
I can also say there is nothing wrong with the controls, I'd take them over CoD's control scheme anyday. They're new and a nice breather from the same old FPS controls.
The multiplayer experience is another beast on it's own. It has an RPG aspect to it where you level and gain new equipement like CoD. I'd say it only takes 10 hours to unlock everything but that depends on how good you are. You don't got to play for days to unlock the best stuff. Overall the multiplayer is well polished and is rarely frustrating. It offers different modes to play and different characters to play as.
In my opinion Killzone 2 is one of the best games out there today. If you don't have it,run, don't walk, to the store. Driving is not optional because you'll need the exercise, you'll won't be getting any soon.