Good
Twas cool. Really got the whole zombie-scenario feel. That was probably the music. It's cool that you're working on pat 2 with more interactive team-mates, that made it all the cooler, that you were defending a house with actual people inside. I loved the reload feature as well. Maybe if the pile slowly shrunk (is shrunk a word?) and eventually you have to change to like a pistol. 2 suggestions, which you've no doubt already heard;
for part 2,
-one of the guys should be another gunner, who helps shooting down zomibies (think of all the archers and stuff on those castle-defend games we're always seeing)
-just put in a little animation for when zombies enter the house (or mall). maybe some feature when they work up the stairs, killing your team mates, and you get a last few seconds to shoot inside the house and take a few more zombies down. Death and glory and all that.
But yeah very cool game, can't wait for part 2.