A lot of the puzzles felt fun, most of them giving me a nice feeling of satisfaction when I completed them. However, I do feel like the ordering of the levels can be changed a little, as the first 2 levels felt a little too challenging to be the first levels of the game, as well as level 3 being essentially a tutorial level. The game may also benefit from offering hints if it helps the player.
I would like to see the ending of each level change a little, maybe instead of just collecting a key, returning back to the entrance or exit to make the level feel a little more satisfying. And maybe its just personal preference, but I did feel a small urge for the character to be a little more floaty, or to jump a little higher. Can't wait to see where this game goes!