I LOVE the concept! The puzzles are really fun to play around! I scratched my head a bit when I saw some of the puzzles! I love the door that reappear, it forces you to have a nice timing. The TAB to skip the level was a nice addition, and I liked the little sounds the characters made. When at some point you have to really think about the order of the cubes, it got really fun for me. I didn't have to just advance in the level but think about the cubes placement. I think the only issue I really have with this is how a character gets stuck on the head of the other one, which makes you lose precious seconds.
Great work!