The demo works fine aside from a few glitches (the special shot didn't hurt the zombies sometimes and we can get stuck on the floor or walls or ceiling).
The music can get repetitive after a while so you should maybe add a mute button.
And finally, i realized i can just jump over the zombies in every level (up until level 5) to beat it so in case this is true on the last couple of levels i didn't check out you should maybe put in an arena where we have to kill various zombies, otherwise i figure people are just gonna do like i did and jump right over them onto the next level instead of beating the set of zombies you put on each level.
And on that note maybe you should give us a reward after we beat the number of zombies on one level, like a power up or something.