Really love the idea. It feels like a first pass on something you could turn into a full game. The physics would need a lot of work and consistency (couldn't beat level 6 even with the example solution), but I know the pain of trying to make a physics engine behave how you want it to behave. There are soo many other block types and variations (like a sandbox mode) you could add, the possibilities are endless! Love it. Have you thought about something like Zachtronics style rating system (like for example in Magnum Opus) where you give player more blocks than are necessary for solving the problem, but once you solve it, you see how many blocks other players used and you can try to beat them?