My first impression, too, was just "meh" ... but then just looking at that pic and seeing those handwritten speech bubbles, the online concept of this actually sounds pretty fun (in a very casual way).
You know all those people that bought a Wii and then never bought another single game. This was the reason they bought a Wii, for Wii Sports.
I know it's probably not totally accurate but the first image that comes to mind is of people swinging their gamepads to play tennis. Silly but effective, I guess.