Most people say that it isn't but I did actually love this game so I think they were expecting something like Grand Theft COD or some other different title.
For 15 dollars its worth it but if you're expecting COD or Halo with zombies thats not what you're going to get. Its the only FPS that I have that I really liked. It has kind of an arcade feel to it there really isn't too much exploring to do and the zombies are kind of stupid and repetitive BUT I really liked that they weren't smart. After all being based off of the show they are supposed to be mindless monsters not worthy adversaries other than their disregard for their own survival and brute strength.
I suppose if you get it and don't like it you can turn around and sell it for 10 dollars anyways so its not a huge loss and it is fun and easy to play. The main thing you won't like I think is when you are surrounded by zombies and they grab you and they take turns grabbing you one at a time and you play a weird mini game where you move a cursor around and try to stab each zombie in the head. Also people have complained about the graphics but I liked them so IDK what they are talking about. Also the game can be completed in the 5 to 7 hour range even during the first playthrough so you might no like that but that was another thing I like about it. I wasn't expecting it to have a long story but I actually liked that you can turn right around and play it again while taking alternate routes to the end of the game.