Nerf it down
I find the game fun and simple to play with. However like all good games, it must be able to challenge the player and make it so that he should be on his toes most of the time. Though I like the traps system very much, I find it "over-powered" even without the ones requiring gamergold (which though I understand that developers need to earn some money for their efforts, I find it unnecessary here; even intrusive I might add.)
The mine placer is a nifty trap which places a single frag mine once every 30 seconds however it is easily exploitable. One scenario is when you rigged the corrider (bottom right) with mines, if done correctly; there is no way zombies could touch you at all. I did this once and was able to leave the game on for 2 hours without any health gone as my trap dealt most of them and my AI partner pick out the survivors.
I could also say that bear traps can be also exploited as after a few rounds, the AI's path is clearly seen as a pathway of blood, by placing bear traps there, you are able to deal continuous damage. Also the barricade is too cheap, on the later levels where you earn almost 100k per round, barricades can be purchased freely and with the added advantage of you being able to walk over them. I find it too "useful."
Also the guns are too overpowered and cheap. I was able to buy the combat shotguns after the 2nd round and upgrade it to the max made the reload neglect-able and the bullets powerful (1 shot 1 kill)
I encountered some glitches in-game, most of the time my teddy bear traps wouldn't respawn and surrounding bear traps around tedd's make them act like a wall. Once in the while, some zombies (same movieclip I assume) may just walk through walls and go over traps (except barricades and bear traps).
Some things that really really bothered me is the lack of the flash-light after the intro. You have the stuff, I urge you to flaunt it! Make it so that some rounds require you to use your flash-light and fight in the dark (while forcing you to run back to the fuse-box and replace fuses in order to get the power up) This eliminates the "camping" strategy most players adopt. The voice acting was of sub-par quality, with little dialogue and did not help immerse the player into the game. Also gunfire became repetitive as it did not have a tonal range. Try to add some "difference," it would go a long way