Considering that you made it in 6 days, I would say that it is a really good game! :)
I enjoyed that when you ran, you couldn't shoot and also that you could power up the shooting, all though I found out that if I just click the mousebutton as quick as possible it works better than waiting it to power up :D Maybe add some extra for the charged shooting, like it would go through 3 zombies or something :)
More weapons and better AI for sure would make the game a lot better but I liked it! :)