Well, one hilarious method for beating the girlfriend levels is to stock up on grenades, and just run around constantly throwing them behind you at your girlfriend...
This game would be fairly fun if the damn girlfriend levels weren't in the game. Furthermore, why on earth would you program her to be dumb enough to run into enemies who will then proceed to kill her in one hit?
some fun hex builds:
-machinegun: misile center, surround by speed, then surround with alternating speed and missile
-Bomb field: similar to machinegun, but with alternating misile and speed in the first ring. You can lay down a dense shield of bombs to absorb enemy fire, and use it as a screen to shoot out from.
A great game so far. I agree that a system of leveling could really make this a ton of fun. And you wouldn't have to add much per level, just maybe a little defense or attack, or just a small hp boost (like, 5 hp or so)