Well done on finishing this game, and doing everything yourself!
Try to avoid having art assets of different resolutions (For example, the characters and the platforms), this will help make everything feel part of the same game.
While I didn't enjoy the sliperness of the character movement, there was some good level design here. Didn't enjoy "leaps of faith" where I couldn't see the platform I was supposed to land on, maybe having a camera that zooms in and out?