The art style is absolutely gorgeous! I especially love the cover image you made, it had me want to play the game instantly! Some things!
The character definitely feels very weighty! try making him fall down a bit slower, this could be intentional on your part but I think you should try lowering the speed of how fast he falls.
The spikes have a deceptively large hit box, and its annoying trying to jump over them, you should try shrinking it, making it a lot smaller. I think it'd even be good if the player clipped into the sprite a bit before dying.
Keep it up!