Great game, and totally free!Graphics are nice, puzzles are just challenging enough, if anything, I make them harder than they are, and your keys replenish with time, so no need to spend cash. There are ways to get free hints in game, or you can buy, but if you really do get stuck, most puzzles are common sense if you work with them, or leave and come back, and there are plenty of walk throughs available online. I have finished one game, have started a 2nd, without spending cash. Play this game!