Decent fun that could be a lot better
The game is a bit addicting, especially with nice clean and fun animation and catchy, movie like music. The weapons are pretty cool, and upgrade option is a very good addition to the gameplay.
However, it does last too short, and it would be cool if choosing one friend over another actually somehow affected the game - or in short, if you had a story going on, no matter how wacky it may be - in fact, wacky is pretty much what we need these days, with most of the games games about zombies being "serious business".
To conclude, you have a very nice premise, awesome animation, and even the sound section is great, but existence of a story (and a longer story, too) almost always brings a whole rank or two more, especially a good one - so for now, a decent rate for a decent fun game. Happy Halloween! :)