Let me try to explain using Wii Sports Tennis.
In the game as it is now:
-You have to swing the remote in the right direction (back and fore-hand)
-You have to swing at the right time for the ball (which aims left and right, like real tennis)
-You can twist your wrist AS you are swinging (can be used for spinning the ball, but it is not very variable)
-You can swing up or downward AS you are swinging (can be used for volleys and shots that only just clear the net.... This one is the extent of the "1:1" the current Wiimote has)
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With the motion-plus, this is the kind of things you could do if there was a new tennis.
-You could hold the wiimote higher or lower BEFORE swinging to get certain shots.
-You could hold the remote still, and the ball would still hit it, which means you could come up to the net and just let the ball hit the racquet for a drop shot.
-The spin control could work perfectly, so you could curve the ball in the air and make it bounce extra high or extra low.
-It could (although the developers would probably leave it out because it would make the game really hard) totally miss hit the ball if you swing too low or high, or the ball could hit the racquet edge.
