Nice one, this is the best of the action games I've played so far. I'm a huge fan of top down Robotron / Smash TV type shooters.
I got to level 7 before my circle strafing all went a bit pear-shaped. Loved the zombies wandering off and leaving you to go for a walk and reflect on what you've done. Top notch stuff :) Maybe throw in another song or two, the main theme is cool, but I think I heard it loop perhaps a couple of times too many.