That was fun, I liked how intense it can get after a few rounds! Unfortunately the game also froze for me after maybe 20 or 30 rounds (I kept choosing the fire rate increase bonus).
Unless you plan on adding more important entities to the game, I feel like the minimap could be replaced by an arrow pointing at the boss on the edge of the screen. I was only using it to aim at the boss but maybe I missed some other ways to use it.
As others have said there are many ways this kind of game can be expanded, I'm curious to see if you get to continue working on this in later rounds. Great work!