Thanks for playing. I have the checkpoints after each mission (10 levels aka tiles) mainly since the tiles are all pretty short and it adds to the difficulty so I don't have to make overly hard levels. There is also the momentum and how tense it gets with having to beat multiple levels in a row where you have to be on edge at all times to beat them. If i could make the levels bigger without any impact on performance, there would be more checkpoints. I'm happy you found the game difficult.