Although I'm a Knizia fan, this game might have been more interesting with another theme. Now it drowns in all the Carc games and expansions. The negative space management is what it keeps interesting.
Usually play this on a 10 by 10 (European?) board. There is a lot more to this game than the meager rating suggests. Granted, it is not chess or go, but it is a very good abstract, with very few rules. The 9 rating is absolutely not a shill.
This game plays well with kids 8 and up. Their memory is 'a little' better, so chances are they know the spots where the -4's are better than the adults. You really have to concentrate well. Not just another "Memory" game.