I like the idea, although I must admit that like Sudoku, it does not really motivate me. Ultimately, it just seems to be solvable by running a standard search algorithm. Why that is not easy to do for human brains, somehow I don't see why I should try.
On the other hand I like Minesweeper, so maybe the algorithmic solvability is not the main criterion. Not sure :-/
BTW, if you play for a while without registration, you can register without losing your progress provided that you still have the cookie that you played under.
You have to click on "submit score" before you get to see the "next level" link. It should be visible all the time, not everybody wants to submit their score.
On the other hand I like Minesweeper, so maybe the algorithmic solvability is not the main criterion. Not sure :-/