Interesting idea!
As others have mentioned, it wasn't quite clear which objects you could move and which you couldn't. The "layer" mechanic also wasn't necessary to complete the levels. I didn't realize I could change the layers until after I had beaten the game and read the other comments. So some tutorial in the game would help, and I'd recommend some more level design to make the layer mechanic more fleshed out and more necessary to complete the levels. I was able to cheese some of the levels by moving the platform and player at the same time :)
The music was great and created a nice atmosphere!
I like the ideas in this one and definitely see potential as a fun puzzle game. Nice job!