It's basically like a "game" version of Picochat. One person comes up with a category and then the other players have to draw their representation of it. The host chooses which he likes best, gives that player a point, and the game starts again.
So I could say "Abraham Lincoln" and then everyone else would have to draw a picture of him. Or I could say "Mrs. UncleBob" and then people would draw a picture of your lovely wife.
I purchased a copy of the game a few days ago for the sole purpose of adding it to my collection. As you said, it will likely be rare down the road, so $20 seems like a minimal investment.
EDIT: Here's the
IGN review. 7.5