I already knew the game was way too hard, but it's good to know exactly why it's hard. I should make more tutorial levels for the mechanics and obstacles, and level 1 should then be like level 4.
I'd really like to slow down the acceleration, but since I'm using the engine's native gravity system I don't know quite how to do it, I'll try to. Slowing down the gravity will make the overall speed slower, but not the acceleration rate, although it might still be a good idea.
I've already got some ideas to not have to memorize all the levels, someone told me to make the camera offset from the player to see more in front of it, and someone else to be able to go back an forth between the start and end if you didn't collect them all, so both things should hopefully help with that.
And I totally agree in that I could've used with more playtesting, I lost a lot of time trying to integrate lighting and ended up ditching it all out because it didn't look good, and in level 3, which apparently most didn't even play, I spent a long time playtesting and nerfing, and probably most just went to memorizing the level, so yeah. It's so much easier to make rage games in game jams...
Anyway, thanks a lot for the feedback!