I never in a million years expected a 3D Mario to be the arguably greatest game of the generation. Both 64 and Sunshine fell flat on me. Then the Galaxy games came along and took both top spots. Somehow, they ended up with the most artistically impressive visuals and the best audio of the generation, along with the finest gameplay the 3D platformer genre has seen.
It will be tremendously interesting to see if Nintendo can produce something equally fantastic with 3D World. Personally, I'm expecting more of a Zelda development from here. Absolutely fantastic games, and by most means better than the "golden" game of the franchise (OoT for Zelda) , but never managing to be quite as terrifically engaging.