I found that the graphics were cute, I personally would have strayed away from mixing differently sized pixels, however that doesn't detract from the game at all.
the puzzles could have been more fleshed out, as I found myself easily beating them by walking back and forth in the starting positions; I do not blame you though, as it is a jam game. I really liked the little grey things that you could use to pass pits, they are cool.
The mechanic of the game may have been easier to understand if there were a more demonstrative tutorial level, as I found myself confused about the game until I read one of the comments. It really isn't intuitive for the player to know that the character in-game will jump through the obstacles.
I found myself being able to get stuck on walls by walking into them, which I assume is a bug that worked in conjunction with the broken restart/menu button on level 7.
Nice job on the game man!