Good first game. Here are my thoughts:
- Character moves a bit too fast I think
- Camera moves in such a static way, no panning, no smoothing, makes it hard to follow the character.
- Level 3 blue ramp down overlaps with the ground and it doesn't look pretty at all, might want to re-layer it.
- Level 3 where the 3 enemies roll into each other from the top and the sides, the left enemy doesn't kill you while the others do, which is weird.
- Music/sound would be good.
- Jumping is not good when touching/moving towards a wall.
That's all, I believe, polish these and you'd have a solid game :)