COD World at War

What in the name of God made Activision and Treyarch decide that a Zombie mode would be good for a WWII game? And what is the fascination with all the Zombie games here lately? You've got Left For Dead, Dead Rising, Resident Evil 5, and now Call of Duty World at War. I don't get it I guess. I feel that COD WAW could stand on it's own without a zombie mode, but it may very well prove to be successful. Who knows? COD4 is a brilliant game. I'm still playing it today and I hope this zombie mode wasn't just tacked on to try and get some people interested who wouldn't have been interested to begin with.