The perfect example of a fair but overrated game.
Anyway, good points:
+flashy graphics, catchy music
+Some nice challenge in the harder sessions
+Multiplayer is some fun
+Some nice flashbacks to older classic games.
-singleplayer is WAY too short
-Price is too high
-A bit kiddy
-low replay value
So what's it all about? It's all about microgames. An example: As Link, use a swift move to pull the master sword out of the stone. Basically, all you have to do is to make a move with your remote within a few seconds. This sounds fairly easy, but it goes faster and faster, and eventually gives you a good challenge! There are some variations on this, but not many, and it won't take you long before you discover everything.
WW:SM was the first of many minigames on the Wii, but it is one of the better, certainly more original than Mario Party.
If you're new too Wii, try to rent this or get it second-handed, you'll surely have fun with it.