Doesn't seem that you can aim down or up meaning you will only be able to hit the zombies from either the left or right
The some of the upgraded weapons don't seem to be anymore powerful (Shotgun), fires slower, and takes longer between shots
There were times when the controls cut out not sure what the reason was. WASD stopped working (though the arrow keys did work) and I was unable to fire or reload any of the guns. This happened for 30 seconds or so and then the controls started working again.
Music, art, and idea were all pretty solid otherwise.