Cool idea and well executed.
While being able to "undo" one step would have been nice (in order to not redo the whole level if you mess up) would have been nice. However, I totally get that this is a jam game and you had to prioritize.
I picked up the basic mechanics pretty easily, but I had a hard time figuring out what the green squares did. I think I solved the first two levels with them in it without using their powers/mechanic and then I got lost.
Otherwise, I really liked the pseudo-pixel art. And the animations looked really good and felt pretty polished for a jam game.
I also agree with you that focusing on art style and game mechanics, rather then menu/pause etc was probably a good idea :)