Very cute mechanic. I love the use of height as both a benefit and an obstacle.
Brutally hard, which I don't mind, but I would have liked more frequent checkpoints - it's too frustrating to die on a section only to have to repeat the previous section again to have a chance to play the hard part again. (In a game like this, I would want a checkpoint in every "room", so deaths are cheap and the challenge is "can you do this once?" not "can you do this sequence of rooms perfectly.) though I realize others may have different opinions.
Also the platforming did not feel great or precise - it is too slidy for me and the gravity is too high. (The section where you have to quickly make blocks to cross a large pit of spikes should be quite simple to do, but I found it infuriating because the horizontal motion would slide off the end or not move far enough causing the block to go up on top, then I would have to jump and risk sliding off again.)
I think this could be an awesome puzzle platformer with some polish and playtesting!