Even for a demo this was really lacking, the actual weapon does nothing to the zombies and you'll be lucky if you even manage to kill an enemy before he kills you first, so i looked through the comments and i saw that i can just run past them and beat the game...
Also what the hell does the potion do? Does it give you back health? Does it make you stronger?
And what the hell was the red enemy for? Was he stronger? I have no idea, i just kept walking away like it wasn't my problem and i beat the demo.
Why were there areas that had no enemies or anything? The pointy rocks looked like they would fall but even that dissapointed me, i can actually just press the right arrow key for about a minute and a half and i beat the game. I hope the actual game is much much much MUCH better.
Polish the graphics, make a story, add some colour if you want, give us a useful weapon and THEN i might actually enjoy it.