Boss. All the way. However I found a few quirks. First, the fast zombies can't be killed with some weapons if they happen to reach you, so you end up having to drop the weapon you are holding or use a killstreak just to kill it. Second, the achievements (besides rampage) are quite easy to get (though this may be because I am a pro) Add more achievements and/or make them more difficult, and fix the fast zombies and this game is perfect.