Beautifully done. The music was very relaxing and fit the game well. It makes you either memorize the layout or re-strategize the order of pickup. The overworld was such a nice touch. The levels were well designed and aesthetically pleasing and it was challenging without being unfair.
My only, tiny nit is that I think having wuupuu start facing left or with some kind of sign next to him would help the user figure out which way to go. My intuition is always to move right in platformers, and I thought the premise of the game was just jumping around in the dark for the first minute before I realized there was a whole puzzle in the next room over!
Seeing just his eyes glowing in the dark is a great touch.