Top trailer! I'm not into games much, but if I was at all interested in something new, this would certainly attract me.
I am usually very grumpy about anything which is a trailer because on Newgrounds it is so often a trailer for something that is never made/finished, but since you have something to play out there and this is reasonably entertaining in itself, I am more than happy with it.
The animation is limited by the gameplay, the voice is hard to hear at first, though it is fine thereafter, and hordes of zombies to fight is not exactly an original idea, but still...
4/5 is as high as I ever give for something which is actually an advert for something else, elsewhere but the sound, art etc is all fine.