The entire Kinect Sports series seems to be free right now, it was like $15 during the Xmas sale on MS' site, but free for now. Obviously, GotY material, and this is gold, so run, don't walk.
Yeah, so anyway, it's free for now.
Update: This may just be a giant demo. If so, my apologies. I deleted this post, but it's still here. *shrug*