Very good atmospheric music, a great character sprite (I kind of wish the walk animation played faster to match the walk speed better) and good puzzle design. There were some points I felt I needed to address though:
The level intro text appears very slowly. I stopped reading it because I'd already be trying to go for the puzzle. Something like [space bar] to complete the text instantly would've kept me reading as well.
An interact button for levers would have been welcome, as I kept flicking the lever twice after turning back, closing the door again. Character movement speed sent me just past the levels usually, so an interact button would've been welcome.
It was pretty frustrating when I've made the level unbeatable by accidentally pushing a crate just a bit too far - the ability to also pull crates back would've been great. Restarting works as well, sure, but with failing jumps and such it added frustration.
Speaking of said missed jumps, the jumping sometimes seemed unresponsive, or maybe a little laggy. It's a common mechanism in platformers to have a brief grace moment after getting off a platform where you can still jump, and that would've been very welcome here, as I think it registered my jump just beyond the edge and I was already falling down then.
In the end I didn't finish the game as I just kept missing jumps, but I did feel bad about not pushing through. After a series of missing the jump, pressing R, missing the jump, pressing R, missing the jump, pressing R, I just couldn't bring myself to continue.
And finally a pet peeve of mine, the art seemed to have been scaled up by 1.5 or something, distorting the sprites. I really liked the character sprite but I feel like I didn't get to truly see it as it was designed. The brick environment art also shows this, sometimes having 1 and sometimes 2 pixels in between each row. Always scale pixelart by whole numbers like x2, x3 etc, or the art will be distorted.
Props for a solid concept, but those elements I mentioned put together kept me from finishing.