It was pretty good, but some things were weird...
My first reaction when I was playing was "why the hell are there no zombies?", the answer being that they were all offscreen and there was no hint that the screen moved only when you got to the edge. My second reaction was "wait a second, why am I shooting with the mouse if I can't even aim?"
I gave up on the 4th level because some gameplay elements are just stupid, and shooting generators with batteries sounds stupid, wouldn't work, and is just a really annoying side factor when you're trying to kill zombies (which is what the game is about).
Anywho sorry if this sounds mean or anything, but I liked the growth system and think you should put hella more upgrades in there for your next game (if you make one). Work on some gameplay mechanics (aiming, no generators, etc) and you'll have yourself something really good.