The basic idea of the game is to get more stones on your side of the board than your opponent. Simple, right? Yes, but to win you need to imply a great deal of strategy. Therefore this is a game that promotes the use of critical thinking skills.
I alternated between playing against my 6 year old and 9 year old for a few games. When playing my 9 year old I played to win. Yet I lost both times. Hmmm. Looks like I'm a bit rusty and need to use my own critical thinking skills!