I was a big fan of your first one, but this one has several problems. When zombies die, they seem to get bigger or something, you may have forgotten to shrink the graphic or something. Whats odd is that this is not consistant, different zombies die at different sizes.
The movement is horrendous. It does not stop when i let go of the arrow buttons, and it does not let me shoot until I stop moving, which has repeatedly left me in the middle of a swarm of zombies. It may be better to code it so that he stops walking exactly when you let go... unless there is something wrong with my computer controls. just an idea if that is the case.
Good job on the graphics overall though, and the shooting is pretty accurate.