The pixel art style looks really good, the colours choice is [a word other than good because I already used that but one that means the same thing].
I also like the hidden tutorial is really well implemented. I like the level where it first introduces the spring mechanic.
Minor nitpick: the whole game uses the cog physics.. except for the animation when you complete a level, the cog just flies through the door thing lol. It kind of sticks out.