A great purchase if you want to play such games as Super Mario World and Mario Kart 64 on your wii! these games are simply downloaded from the virtual console (nintendo's download service), you plug the Classic controller into the same port as the Nunchuck- and game time!.
Not all games on the Virtual Console require this controller to play and instead use the side on wii mote. However Some games are only playable using it (arguably a cash in by nintendo). but the controller looks and feels great- so it is worth getting one!