The animations are good and there are some good details which give the game some character (the day/night contrast, the landing sound after a long jump, character running around in the start screen). The movement/jumping is smooth.
The MS Paint style artwork is inconsistent. I imagine it's just 'filler' art that you're planning to improve.
"W" would have been a more natural button for jumping IMO.
There was nothing original or special about the gameplay.
Good job overall for a first game!