It is amazing how my brain defaults to "Red in Red Bucket" and I appreciate that you tried to make me break the habit. I love the art!
It would be nice if the rings started blinking before the last bullet that could hit them. Also, I would love a clearer indication of when the collection round is going to end, because I found myself feeling a little like I was just waiting for it to happen. Some sort of meter would be great.
I also would love for this to be a little tougher! The boss fight could afford to move a little faster and have more attacks, and some sort of loss condition in the start would really amp up the stakes. (I totally get it though, Jam entry).