The main idea seems cool, but there are a lot of annoyances. As was mentioned the second wave looks unbeatable. And the first wave is trivial (at least with the choice of increased fire-rate). Therefore to even try to defeat the second wave you need to go through the "tutorial" of the first wave again.
I would also like the collisions to work better, I spend a lot of time around the base (circle/elipse), but the collision box is a square/rectangle. And it would be nice to have an indication when the secondary lasting-area-damage is ready.