Can't go wrong with the Robotron formula, and it's always nice to see a take on the genre that makes you think a little about how you're shooting. Might be interesting if you could get more points or something by keeping enemies big for a while as the current system heavily rewards killing enemies in one go, which you'd probably do anyway.
I appreciated that the projectile enemies didn't spawn every wave since they're more stressful and not having them around for a wave or two gives you some breathing room.