First I really like the touch of that dither fade between the title cards. The art in general is fantastic, and the soundtrack and sfx work perfectly.
I think this is most of the way there for a rage game, which is great! I do think there are some pitfalls, though.
The big one for me is that the friction isn't quite right. For the most part it works fine, but there are particular segments where moving elements cause the game to not detect that the ball is "still" for an extended period. At the 10M flag, for example, I manage to get the ball on top of the rotating block that didn't have slime on the top... and then proceeded to get softlocked because the ball just kept rolling slightly back and forth as the block moved around, and was never still enough to let me jump again. The same thing also happened on the L-shaped block above those two, where I landed inside, came to a stop, and then the movement of the block both prevented me from jumping and rolled me off. This is frustrating in a way that doesn't feel "earned" by the game.
As others mentioned, the difficulty curve at the start feels too high, largely because of two factors. I think the beginning is maybe the weak point of the game primarily because there is no quick restart button, and especially because the spot that you start from is very difficult to get back to.
I think the difficulty curve in general feels a little skewed - I think the first two sections are much harder than the next - it only took me two tries to get to the flag just after 30M, but it took me much longer for every section beforehand.
Unfortunately, the checkpoint after 30M is where I had to call it. There's too many submissions to spend too much time, but also this game does something that most rage games avoid, and I think they avoid it for good reason - cycles. At a certain point, it didn't feel like the game was respecting my time, simply because I was spending so much of my gameplay just staring and waiting. At the spot after the 30M flag, I missed one jump and then had to wait a full 15+ seconds just... waiting for the moving block to come around again. I'm perhaps biased because I have a distaste for cycles in just about any type of game (the cycles at the end of Shovel Knight are one of the few major flaws of the game, fight me), but I also think that most of the popular rage games (Getting Over It, Pogostuck, Only Up) pretty much avoid this type of mechanic entirely.