Highly addictive, challenging, LOVE the music, can't stop playing it. Absolutely PERFECT! I am editing my orig post 'cause I was mad that the hint system solved the level rather than giving hints. I was wrong. Just hit 'pause' and return to game and it puts you back on your own but you can still return & continue with hints (using the same hint expenditure) until it's solved if you want to, or any where up to then. It's actually very well done but wasn't obvious at first. Note that the hints are obscenely expensive though. Yes, you get four free and can get more by tweeting and posting on FB (brilliant idea on the part of the Dev, BTW), but then for four more 'hints' you pay the cost of the game! Or you can get 12 hints for twice the cost of the game! A bit much IMHO. Oh yeah... the full-screen, game-blocking advertisements are THE most annoying of any game ever and they are absolutely incessant. So just buy the game. It's absolutely worth it and I should have just bought it after Lev 20 'cause it's a lot of fun & great brain exercise for the little cost. I LOVE the game and the music is as addictive as the game is. Kudos to the Dev.