Negative feedback is the best kind in development, though.
Damn, I've only ever bothered to go to wave 52. But yes, this is a development build and there is no end-game progression at all past the three bosses. One thing at a time.
The upgrade system is really just a placeholder until I make a final decision as to what stats should be upgradeable and how, but they likely won't stay percentage-based.
The turret AI is as it should be. I was planning on implementing a perk / talent system, and one perk could be to change the turret AI. They aren't meant to be perfectly efficient killing machines, or it would make things too easy on you.
I thought I had corrected the ammo buying issues, but I'll take a look at that.
The framerate issues should probably be expected after a certain point. The number of enemies in a wave grows on a logarithmic scale, and at wave 100, there would be about 670 enemies. I've only gotten to wave 52, but I think I'll have to modify my wave-generation method to spawn on-the-fly as opposed to all-at-once. Also, I would guess the CPU usage issue is because there's a pretty hefty amount of trig functions being used (I really need to convert to vector-based movement and only calculate new vectors when needed).
Thanks for the feedback!