BLLEEGAAHHH!!
I don't care what you said about the voice acting; it's part of your movie and is to be used to determine the overall quality of the piece.
The voice acting was pretty bad. It didn't seem like they were threatened. The last line of the cartoon was pretty funny, which probably wasn't intentionally so.
It didn't make sense to me without having my own ideas why they didn't bother to let the guy in. Judging by the fact that their windows and door were boarded up, it's obvious they know about the zombies. So the fact that they were just like "What? Huh?" when someone ran to the door screaming "Let me in!" when zombies have been running rampant is pretty silly.
The violence and action was okay, but there wasn't enough. Usually with violence I fall between the idea of a little bit of fantastic stuff, or a lot of some pretty good stuff. This was a little of some pretty good stuff.
Art-wise, the people looked a little odd at times, but otherwise acceptable. I didn't like the fact that the girl leaning over the railing at the beginning was drawn overly sexified (especially in the middle of a zombie invasion) and would have been like twice as tall as the guy if she leaned up.
Overall, it was pretty good. If you make another one of these, do more action and make the violence look a little better. If those two fields are any better and longer lasting than what was here, it should make up for any shortcomings it has.