I think Super Mario 3D World is going to be received a lot like Super Mario Sunshine -- it'll sell the same 5-6 million, but it won't quite be the Mario game that fans really wanted (something more in the vein of Mario 64/Galaxy). People are pretty harsh on Mario Sunshine though, relative to the size of the GCN userbase it sold pretty well and has a Metacritic score of 92.
Also I think Nintendo's habit of making equivalent portable and console versions of the same franchises (ie: NSMBU + NSMB2) released in 2 years or less between titles is a mistake on their part. It creates brand saturation and worse creates the impression of "I already have this on my 3DS, I don't need to buy a Wii U for that" even if its a "new" game.
Mario saturation in general I think is going to become a bit of an ugly problem for Nintendo in the next couple of years if they don't start trusting/pushing other IPs to sell systems.
Metroid Prime was also a pretty huge critical darling for the Gamecube in 2002, a lot of the major gaming press gave it Game of the Year honors and a sky high reviews, so it added a nice amount of prestige to the GCN, even if it wasn't the Halo-equivalent Nintendo was hoping for. Animal Crossing, Star Fox Adventures, and Resident Evil 0 weren't too shabby either.
