Very fun gimmick, and actually solid gameplay built around it :)
Would love to see other bosses and enemy types added, the game works beyond just "cool concept woo", I think it could work as a rather fleshed out game.
Could use some optimizations, the homing shot in particular makes the game stutter a whole lot once you have fast fire rate and large spread. Other than that though, what's in this build is really fun.
Here's the score from my third or so round, maybe all the Geometry Wars helped me a bit here. (I had to just give up eventually, the game got way too slow to be very playable, and I'd reached a point where it was pretty much impossible to lose. 3 bosses would spawn at a time every time I finished them off and the second my shots started homing in the game would get super stuttery.)