Wow TD, cool! The game is funny=).I liked that you could practically create weapon everythere. I got to wave ten=). The only thing that interrupted my progress was that I upgraded the hammer=), and after that, I lost the ability to perform building.
Also, perhaps you shouldn't require the player to constantly hold down the E key for the upgrade action. It might be better to have the cursor chase the icon and let the player simply left-click when they have the money, without fading BG.
Great work!