In terms of fun this is one of the best ones I've played from this jam. I ended up playing for a while actually. I gave up on the third phase of the boss though because it got so crazy and I kept dying. In terms of feedback, I think the main problem here is the fact that if you start doing worse, it snowballs out of control, and then you can't recover. So in a sense you get soft-locked, because you've messed up and will inevitably die, but you haven't died yet. You can't always tell when you're doomed either, because (during the boss) all it takes is like two or three upgraded enemies to do the trick. It looks like you're in the clear, but by the time you can kill them, five more have joined together, and the boss's health has filled back up. Even then, I still found myself attempting to save the situation. I think it's good game design to avoid soft-lock situations like that.
But other than that, this game is really good. The concept is clever and I found it really enjoyable to frantically scramble around trying to keep the enemies apart. It definitely has that "addictive" quality to it, something a lot of game devs attempt and fail to achieve. I think with some adjustments this could be extended into a really cool full game.