This is a pretty decent game. However, after playing through it a few times, I'm going to have to agree with everyone else. Once a zombie reaches the door, you're dead unless you have explosives by that point. However, getting mines or explosive arrows by day 3 (which seems to be when most people, myself included, get overran) requires perfect accuracy. Ironically, that would remove the whole "a zombie got to my door on day 3" problem.
On a lesser note, it's just annoying to sit there and wait, if you don't have the explosives. No one likes to wait for an inevitable failure.
You did a nice job on the art, though, and other than a few problems with the difficulty curve, this is a pretty solid game.