Definitely worth a buy!
Anyone that owns the game and is at all disappointed and hasn't gone through the second time, then TRY IT. Go back and play through the story modes again. There are still a ton of hilarious microgames (not to mention multiple boss battle difficulty settings) that you can unlock. DO IT and you won't be disappointed.
If you have ever wondered how much your wii-mote could do, then pick this up. You'll be amazed at how much this game alone proves the Wii's motion sensing can do.