Minor one but useful: it would be convenient to have controls hint in the game.
Jumping feels floaty.
It's easy to get soft-locked by incorrectly moving crystal
It's sometimes impossible to avoid enemy hitting from ceiling.
Platforms in some locations are out of screen and you have to jump in nowhere hoping for best luck.
I saw only one checkpoint but death happened more often even after some retries, it would be nice to have more checkpoints.
Character and enemies look small compared to big empty halls. Or vice versa: halls enlarged and lonesome compared to relatively small charaters and action. To my taste, the scaling can be improved in either way.
In general, I liked the concept of reflecting rays and expected relaxed puzzle-like gaming. However I mostly struggled with jumping on platforms in exact way game forced me to.