Really fun game, I wish I was patient enough and good at platformers to go the end.
Theme:
Definitely minimalistic game, it's not a perfect theme interpretation, but works :)
Visuals:
Visually game is beautiful, I really like postprocessing and glow you have used, it really makes this minimalistic game beautiful. On jump character squeezing is also great idea, adds a lot of life. If I were to advice something, maybe it would be good to add some screen shake on landing and hitting objects like spikes, opening doors. Also some particles while moving, landing might be a good idea. Apart from that really nice.
SFX:
It was pretty ok, maybe if you could make the music loop a bit better it would be perfect.
Gameplay:
Very enjoyable, I like the movement and challanges we are facing. Maybe it would be good to make falling a bit faster, as it was sometimes annoying (or add contol on 'S' to quicken landing).
Game Design:
Game leads player pretty well, puzzles and levels are interesting. I would just suggest to make checkpoints room related. When I was dying on these wall jumps with spikes, I was taken all way back to previous checkpoint and had to go far way before reaching next point, and I've died many times there. It caused me eventually to quit the game. If there was 1 more checkpoint, it would totally change my attitude (it's not good to make player repeat part of the level he already beat.
Very nice submission, I wish you had more rates. Good luck :)