i agree with Taranos. It's a utterly bad game!
*faceslap* man really? Do I need to speak out how utterly bad, cheap and 5 minute work this is or you know it yourself?
No sounds, No music, No story, graphics could be better, it is a start I hope to see improved versions in the future :)
We've seen this type of shooter many times before, so you'd really have to add a new twist to keep it interesting. At least you have a solid base to build on. It ran smoothly in Chrome.
I noticed that when you walk left and stand still, all zombies suddenly start coming from the right (a single entry point of the arena?), making the game play/zombie movements too predictable. I imagine arrow keys plus mouse works well for left-handed people ... but you should either include the option of WASD controls or make the controls configurable.