Pretty good game
Complaints:
Aiming, this really needs in improving. I've had cases where I aim for a zombies head and end up shooting at the feed of zombie that passes by the one I'm currently killing.
You might also want to consider throwing in a difficulty setting. I've played this before and after you updated it. I can tell you upped the difficulty for those who complained about it being easy. I really wish more flash games would use difficulty settings. Not everyone will be happy, more like 80% tops, but its better then having half the pool of players bitching about the game being to0 easy for them, or being too hard.
Add some different choices in music.
Be able to blow the arms off of zombies, and the limbs off of the dogs. OK that isn't really important, and it might be asking too much.
Compliments:
The style was great and so was the graphics
Variety in the number of enemies, and how much of a threat they posed to you. This killed monotonicity of killing zombies. Plus, it added an element of strategy, like blowing out the legs on swat and soldier zombies.
Humor was awesome. Especially, the lone clown zombies. I enjoyed the few times where I successfully removed his head with a well placed shot.