I like free-motion games because you have a sense of freedom in the way you play. The player is able to move around somewhat freely compared to just being limited to a controller. Free-motion games also, quite obviously, are very active; so you at least burn some calories whilst you play.
I reckon that in later years, free-motion games will be taken up a step in terms of technology. As in, the body's movements are captured more precisely and games will be able to be played more accurately e.g. in Wii Sports 2, you just kick a ball however you like and it goes in the same direction; but later we will be able to kick the ball and it goes in the desired direction or us kicking it in a certain way and affecting the ball's movement.