At first, it seemed like a really simple game. Classic FirstPersonController, collect 4 things, e.t.c. But then, the **level design**. My goodness this was nice platforming. I wish I could think of such intricate levels. And the fact that you made it so you need to use prior level knowledge to beat a new version of the same level is even more impressive! I think you hit the mark regarding theme and mood, and with an update on graphics/textures this game would be amazing. And then where I least expected it the ending happened. It gave me the chills. Nice!
I have some things I'd like to complain about though. The breathing animation can be a little annoying and makes me think I'm going sideways when I'm actually going straight. Maybe that's part of the game though since you are supposedly going mad or something (it's not a bug it's a feature style). Lastly, the colliders on some ledges are a bit iffy and you can get stuck trying to jump from floating ledge to floating ledge.
This game was a pleasant surprise! Good job.