A simple, yet highly addictive game.
The game's goal is simple: destroy the yellow circles or capture the golden rings. All it takes to play is being able to add numbers no bigger than 9 and some strategic thinking. Once you beat the first few levels, you are most likely hooked, and it will be hard to stop until you have at least beaten the game once.
If you create a new game on easy, it won't even take you an hour to beat all 40 missions with a gold medal. Then, if you create a new game on medium, the difficulty is approximately that of the middle levels of easy. And by the end of medium you face some tough levels. And if you create a new game on hard, the first level will be about as difficult as the last level on easy, and they quickly get more and more difficult.
Sadly, there isn't anything to do except for the 120 levels. That is, in my opinion, the game's only flaw. It is so easy to think of some achievements for this game, like: beat a certain amount of levels within a time limit, or within a rotation limit; beat each difficulty level and so one. But Gameshastra chose not to. Too bad.