From a visual / level design perspective, the dark level was the best one out of them all. I wish you would have explored more ideas like that, instead of the levels leading up to it. But something happened in this level, that I don't understand if it was by design or not: I hit the skull, instead of the button, and it looked as if I won? Or at least, I got sent back to the menu. Either it was a bug, or intended. If the latter, the information could have been communicated better. The camera was also not optimal, but it was serviceable.
All in all, it was a fun & quite polished game. Good work on sticking to a central mechanic and delivering :)