Very very fun!
I really enjoy the wild chaos of this game and the music choice was a great fit that added to the game's upbeat nature.
When it comes to the enemy A.I., The A.I. for the "C" enemies behaved a little strange as they would mostly just stand motionless and be free kills, only some would start shooting. However on the other hand the "B" enemies were incredibly fun and I absolutely loved their behavior of jumping around, it added a lot to the fun chaos of the game.
As for bugs I only ran into one at the start of the game. When the blue info panel pops up the empty score bar appeared over top of it and made it difficult to read the start of the text. Everything else was polished up very well!
But overall I had a lot of fun with this one! I find that a lot of others, myself included, took the more dark and serious tone approach to the "echoes" theme so it's really nice to see the more upbeat projects.