The game is really good indeed, especially since it's your first. However, it's not just about challenge. It's fine to have to do levels over and over again to find out how they work, but doing every single level over and over again when you die, that's just punishing the player. Even though it seems to be against your principles, I suggest you seriously consider to only redo the level you're on. Or perhaps do a checkpoint every 5 levels.