Which One Should I Buy? "Call Od Duty 4" or "Killzone 2"

[Rishay-87]

I Already Bought Killzone 2, but, im scared to open it, lol......I'm just not sure whether its better than call of duty 4.
Any Suggestions?

EDIT: I Already Have Quite A Few Shooter Games....Is Little Big PLanet Worth The 60 Dollars?

THANKS...........