Thank you for your nice feedback! The music was actually royalty-free, but I was scrolling for a while to find something fitting for the game.
Regarding the controls, there definitely will be an option to change key bindings, right now I kept it as I'm used to playing platformers, but honestly, the default should be WASD/arrow keys and zxc, not jkl.
The long-term goal is to make a more clear split between puzzling in light form and platforming in the shade form, and add a lot more story. There probably will be moving boxes, levers, mirrors reflecting rays of light (and preventing the shade from crossing?), there are a bunch of ideas we're eager to put out.