I think that you should add wasd also for moving
But the main thing is that you need to make the character move/rotate about its axis like move the gun 360 so that it would be much easier to control the character !
so that you could move it a different direction and still be able to shoot at zombies
So that you don't move but can point and shoot in any direction
Since there are way too many coming at you.
Also there are regular zombie freezes where they all freeze for a second or to then start moving.
\Don't know it that's a glitch or you made it so that the player could have some time to move away.
And some upgrades to the gun would be nice.
Cus i don't know if you played it yourself to see just how many zombies come at you.
Anywap good job and Good luck further !

It gets boring quick since there is no point to the game. There isn't a goal. It needs a timer or a score system to give players something to play for. Add some sound effects and change the controls to WASD to make it easier to move around. A pause option would be nice too.

Could do with some sound effects, music, background details, blood effects and a whole heap of more features.
The controls could do with some improving also, maybe change the direction you're facing to where the mouse is pointing on screen and move the character with WASD?

Not Bad...

I would request allowing the user to move backwards and I would also like a reset button so I don't have to refresh the entire browser. Mayyybe even a story of some kind :)

Keep up the good work.