Zombies, zombies, zombies!
I'm a big fan of zombie games and movies. It's a genre that didn't really get much attention up to a few years ago.
As for your game, I really enjoyed it. I love how you used the old sprites from the Metal Slug series. The music was creepy, the graphics were smooth and the gameplay was decent enough. Unfortunately, I accidentally blew myself up with the trip mine before I was able to get too far into the game. I think a couple new weapons would be good, as well as faster reaction times when you want to stop shooting and do a quick 180, but then again, I guess that really comes down to the skill and timing of the player, and isn't really a fault per se.
Cool idea. I am curious where you got the sprite for the hero character. I don't recall seeing him anywhere, perhaps you created it yourself?