This was great :)
The game looks good, and I love the music. Didn't expect that shadow world thing, it looks very cool (and the music changes too!) and made sense. Puzzles had quite a few mechanics and felt good.
Only complaint is I thought the walking speed was very slow.
Since I saw you ask about the difficulty : I thought it was well balanced BUT some of the levels felt like you needed to "die and retry" to be able to figure out the solution. I'm fine with that but I think some people dislike that.