You know, the rule to kill a zombie is by destroying the brain. This concept has been completely discarded by the maker of this game. Instead the way to kill an enemy is by shooting one of two spots (either the area from the waist down or the neck). But the flaw in that is that when you have to kill more than 5 enemies, the floor gets cluttered up with bodies and you can't hit either of the spots. Making you move to a more clean area, which is hard to do, because when a zombie hits you, you get pushed back.
Furthermore, the laser does not go through multiple targets, which seems odd to me. Since well, it's a laser.
If multiple zombies charge at me, I have no other option then to hit one and jump over them. It's even the case that the zombies actually go into one spot (while coming to you), so when you take one out, it seems like it doesn't have that much effect and you have to do it 5 or 6 times more before they all fall down (and you do this without knowing how many there are, since they are all cluttered together).
All in all, I think this is a poorly implemented game. The gameplay is downright.. annoying (and doesn't make sense). And the levels are poorly designed. Thus even for a demo, this is under average quality.