Pretty fun and original, awesome game! I really liked the idea of controlling the momentum to hit enemies, it feels pretty satisfying. If you find ways to variate the mechanic you could make it into a full release.
About things I think might be improved: To start spinning the ball I had to take too much damage since it takes a while. If I keep hitting the dead enemy after he disappears the next stage does't start (it only happened in the final boss. Also, I was able to use the moon horizontally in a never ending loop that killed the boss without me doing anything, since it was hitting him from left to right, it was really hard to do it twice, but it's possible.
Congrats on the game, I hope you try new things with the mechanic since it's pretty satisfying.