Usage of theme here is cool. Even in such a short time I had an "AHA" moment on the last puzzle.
To make the mechanic a little clearer maybe the balls you can walk through should be a little transparent?
I found the mouse sensitivity is very high, If I didn't have a dpi switch on my mouse it would have been a pain to look around.
I think it's cool having differences between the "2 worlds" you go between like how you changed the music. (Maybe more visual differences like post processing/shaders could work aswell?)
However the sound effect for going through the door confused me when I went through the door a few times in a fast succession. Maybe it's better if it was more of "swooosh" rather than a musical idea, it felt like there was suddenly 3 songs playing at the same time.
Sorry for so many personal suggestions, I really liked the idea here!