Phew, I didn't think I would see the end of this! The control are very interesting, and provide cool puzzle. The challenges offered by the game are fun to win, and I definitely felt like I became better as I played. But I don't think the game needed to be that punishing. Starting some long and difficult sections all over again wasn't that much interesting, nor gratifying. Mostly it just felt like the game wanted was wasting my time for no reason, or didn't want to be finished (which is valid too I guess, but it needs to make a point or have an appropriate narrative to work). The fact that there is no indicator of the strength of a jump made some parts kinda nondeterministic, which added to the frustration.
That doesn't mean that the mechanics weren't interesting though! Again I really appreciated the controls, and the puzzles that came with it! Having to deal with wall bounces and slippy floor provided really cool challenge. And to be fair, at some points the level-design felt a bit merciful, with pits placed just so that you woudl'nt fall too far away (that's mostly the case at the beginning of the game).
And of course, I must mention that the art is gorgeous! Really splendid pixel-art with great animations and effects. You did an amazing job here! As harsh the game can be, it's a pleasure to move forward in it just to enjoy its landscapes!