The gameplay is simple, but classic. It'd be nice to have an auto-reload on empty. Having to click for each shot isn't something I mind too too much, but maybe an automatic weapon would be cool as an upgrade.
There's a few quirks with the collision detection. At one point I got stuck inside of a zombie and I just couldn't get out of him and he, well, ate me. Also, it'd be nice to have a play again screen at the end (if there is I couldn't find it.)