Ummm... If you like FPS just buy it!!!!
Graphics: I think it is rather obvious with all the reviews that this game has the best graphics currently available on a console. Amazing is all I can say.
Sound: DTS is a yes please in my book. Surround sound takes a game to a whole new level. Everything sounds so real and you feel like you are actually Sev in the middle of a war.
Game play: Very fun. It is nonstop action that is intense. The game is section after section strategic fighting with the Helghast. The cover system is great and the enemy AI is the best I've seen in a long time. The way an enemy falls when they get shot also depends on the gun, the range, where you shoot them, etc. It is amazing!!
Physics: Awesome!!
Story: It is lacking on its own, but if you go to Killzone.com and read the storyline of the entire conflict (encompasses Killzone, and Killzone Liberation, along with the info prior to this then the story is great. The action is more than enough to keep you going.
Multiplayer: Great!! Very fun and entertaining. The squad system is fantastic and puts it above other games. The maps are very well designed too.
Basically, just buy the game. It is awesome. If you own a PS3 you have no excuse not to have this game...plain and simple. Nothing compares to it in terms of a FPS.