Wave 11 is a bitch and 3 bitch pipes, the game gets exponentially harder from there. I love this game. I do have a few minor complaints.
1) Ambiguous upgrades such as the clip size upgrade. My gauss gun has 6 rounds in a clip, is that right with 1 clip size upgrade?
2) I can't access the shop until I beat a wave, and for some of the later waves that's gonna be a while.
3) I would like to see a display of what the gun does when I look at it in the shop(clip size, firing speed[shown in milliseconds], damage, anything worth noting about the gun, etc.)
4)I would like to know what an upgrade does in specific for example: When enemies get near you strike back. How does that mechanic work? Is it automatic? I don't notice it if it does happen.
All in all, great game with minor design flaws that you may or may not look into. The game is fantastic as it is.