Wow
I'm not usually into these kind of games, but this is one great game. This could have easily been just another zombie game, but somehow you managed to make it special, and I really enjoyed it.
However I have 2 things that I want to suggest:
1. The last weapon that you get seems too powerful. Once I found it, the game seemed way too easy. Maybe you could reduce the amount of shots in each clip and/or increase the reload time. That might help a little, but the fact that it kills everything in its line of fire seems too cheap to me.
2. I don't know why, but the ending seems a bit weak for such a great game. Maybe it's just me and my perpetual desire for a solid conclusion. You did hint that there may be be more after this, but its not just that. The last level seemed just like every other level except maybe a little more difficult. Of course I couldn't really notice the difference since it seemed pretty easy once I found the last weapon ;D. Maybe you can make stronger zombies or something right at the end. Ones that don't die in one hit from the last weapon. Just a suggestion.
Regardless of my two complaints. I think this is a great game overall. I gave a 5 for humor because there wasn't much in it. I guess you didn't intend for it to be a humorous game, but I did find some of the zombies' looks and the way they died slightly humorous. That could just be my sick and twisted self though. :D