Very well done good sir!
10's.. mostly all around. I gave the 8 in sound because the sound became repetitive in nature after a while, and I'm pretty sure if the crickets in the background was to here 7 men shooting undead zombies with a variety of weaponry, they might shut-up. Anyway, I really enjoyed it throughout the game. I'm anxiously waiting for a sequel. :-)
The only thing that REALLY bugs me... isn't the bugs.. it's not the 20 level limit...
It's the way that a standard issue military style bullet-proof vest is able to stop a .50 caliber armor piercing round fired from Model 82A1/M107 Barrett... Every time!!! Granted.. it was kinda fun removing the leg from the knee down with an armor piercing round :-)
Congrats once again, on the spectacular creation. I'm impressed that this is your first flash game.