Nice pixel art and music :) The platforming is a bit stiff. If you want every platform to be completely solid with no pass through then I'd recommend making the jump feel more fluid so you can actually maneuver around them. Add things like being able to move in the air and allowing for smaller jumps by just tapping the jump button.
Another thing is the camera, it moves pretty slowly compared to the character. Might want to do a box around the character, and if he gets to the edge of the box then move the camera.
I think a big thing you could do is pick a platformer you like a lot, and then recreate that movement. It gives you a really good feel for what you're actually looking for.
Good job on this submission :)