Good puzzles, and nice mechanic with the growing and shrinking. I'm not sure that the "level up" system (increasing speed or jump) added much meaningful strategic choice to the game, though.
Some of the hit boxes seemed to be too large for the graphics. I was unable to beat the game because, even though I was in my shrunken form, I was still too big to get through the opening.
It would be a big plus to give the main character a bit of animation. Remember that the player is staring at that sprite the entire game.