I like it! Haven't finished stage 1 yet but heres some feedback.
Enemies don't take damage if they're directly in the center of your circle. Often there's a few enemies that are immortal. Completely black and constantly being hit but not dying. Rarely (once so far), 2-3 balls will bounce off the corner of an enemy and either only 1 does damage or none do.
UI: Moving the stop button out of the playing area would be nice, there's a lot of empty space for it up top. I think the after round text is wrong, it says "Player cush" instead of what i assume was meant to be player cash.