I will be posting an updated version soon. New weapons, enemies, and a brand new 'powerup' system that helps make the game a bit easier.
As of now there are 4 difficulty 'loops', but that's all for now. It just gets a little harder 4 times. Eventually it will be more in depth, like different bosses for each loop. The way enemies spawn now can get pretty hectic, my advice is to buy all the bombs and use them for when you are pretty much cornered. Also the soda machine can be helpful in the later waves.