I honestly didn't enjoy Killzone 3 that much, I found the campaign too short, the characters to be very plain and uninteresting And the AI to be very uninteligent (they would get in my way and would run in front of me while I am firing at an enemy, my buddy would tell me to be careful when he was clearly the one running into my gunfire). The story had no parts that I could call epic exept for that one part where you are fighting that massive machine (I forgot what it was called). The split screen was irritating because I found the screens to be very small. In the multiplayer, I wasn't a fan of the maps and the variety of guns. Some good things about the game includes an outstanding graphical achievement, a great feel and weight to the weapons, exelent stealth sections and one of best sound designs I have ever heard in a game.
Even though I didn't enjoy Killzone 3 that much I still tell people to buy the game because the majority of people love this game so at most chances they will love this game too, I hope you respect my honest opinion on Killzone 3.