Really good game! My biggest critique here would be please have what items are under boxes somehow displayed over them. For puzzle games, you don't want to hide information from the player. The challenge should come from the puzzles themselves, not trying to understand the puzzle. I don't remember which level it was, but one of them had a 50/50 between instantly needing to restart the level and the correct path. That doesn't really add anything to the game as all it does is either continue the level, or you start again and continue the solution up to that segment because you already know the start.
With more time for level design, there is absolutely a lot of potential here.