I'm not a very good artist, but I wonder if it would look better if parts of the hero didn't blend into the background. I like the art style though! I was unfortunately too terrible at this game to get very far and I am not sure to what extent to blame the platforming physics.... your sidekick kind of moves like Luigi (slippery, low air speed), and I can't necessarily say it's wrong but a lot of people seem to have difficulty with it.
I had enough fun to lost a few times in the same place, and I appreciate that you made everything by yourself! Thank you for sharing your game.