I think most people consider SMB2 the black sheep--I know I do.
People say it's because of Fludd, but I think it's because, unlike virtually every other game in the series, it didn't revolutionize or perfect anything. SMB was the first 'true' sidescrolling game, SMB3 and Mario World were 'perfections' of it. Mario 64 revolutionized 3D gaming, period. Galaxy (arguably) did it again with the gravity system, but more importantly it is perfection in the platforming genre.
Mario Sunshine... introduced Fludd?