There is a rule in minesweeper, which is that the board is generated after the first click, and that the first click is always a blank tile. This is to guarantee a workable start state. This comes to mind because of level 6. In five or six attempts, I had exactly two viable boards, and one attempt I clicked a mine before even having an actual start. The fact that being able to start is random, and that a single attempt might take half an hour, is frustrating.
Otherwise, this is a super cool game.