First of all, thank you so much for the detailed feedback! I really appreciate you taking the time to explain what worked and what didn't.
I completely agree that the game is too dark. I wanted the darkness to be a major part of the experience, but in hindsight I pushed it a bit too far. A brightness setting or simply making the darkness slightly more transparent would definitely help.
The inconsistency between the mechanics is also a really good point. The game originally wasn't meant to be a puzzle game at all, it changed direction quite late in development, shortly after I had implemented the skull enemy. That's why some of the mechanics don't have as consistent a role throughout the game as they probably should.
The skull was originally supposed to be a "Listener" enemy. Whenever the player made noise, it would detect them and search around points near their last location. When I changed the game into more of a puzzle game, I didn't want to completely throw away the enemy I'd already made, so I gave it its own level. Looking back, I definitely should have done more to communicate what it actually does.
I also agree with your point about Level 5. The solution is intentional, but I didn't have enough time to properly communicate the rules that make the solution possible. Some players figured it out, while others understandably thought the walls were just a bug.
The game definitely needed more time in the oven. There are a lot of ideas in it that I would love to develop further, especially the puzzle design and how the mechanics are introduced and combined.
Thank you again for the feedback! It's honestly really useful to hear this kind of detailed criticism, especially now that I can look back at the game after the jam