I've just tried the Wii fit plus ... and it is gooooooooood!
I didn't realise but it contains ALL the original Wii fit, so if you have neither just buy the new one!
It also uses the data from the first one, so it already knew all my details!!
I haven't finished trying all the new stuff yet but I've had great fun with about half of them. And now I'm nackered and going for a bath haha