My problem with the levels is not that they are not challenging enough, but that they feel incompatible with how the character controls. If I were to design these levels with the current character's movement in mind, I would probably get rid of the enemies altogether or just make them die in one hit. I would also get rid of the puzzles and replace them with pure platforming challenges. That's because I would want the game to focus on speed and precision rather than solving puzzles. If I had to make a character controller with these levels in mind, I would probably make the player character and enemies slower, and give the character smaller jumps. Don't take my word for it, cause I have no idea how these things would actually affect the game in practice. This is just my opinion, and I also have limited experience in designing platforming levels :)