Challenging game! Actually, the controls were good, that's just the velocity that is hard to control.
I have a few remarks about the gameplay part :
- I was frustrated of not being able to go fast.
- The difficulty curve wasn't balanced as the hardest part was the beginning.
- The hitbox is way bigger than the character, while it's usually smaller that the character in many famous games. In my opinion, that's not a good way to add challenge, as that only adds frustration (a good example of what I mean is the World's Hardest Game's hitbox).
Also, I would recommend to avoid using mixels (different resolutions of pixel art on the same artwork).
I didn't really get your interpretation of the theme. For the limitation, I understood it thanks to the other comments. I think you can make the text grey on black, but give it a bit more contrast, as that's really invisible if your screen luminosity is low, and also bad for accessibility.
Nice level design.
Good Music!
overall nice!