I like the path Mario is on now for the core series. I wasn't super thrilled with the franchise from Super Mario 64 to Super Mario Galaxy.
But Super Mario Galaxy 2 completely blew me away. It captured the spirit of the original Mario sidescrolling platforming titles perfectly, but as a 3D adventure platformer instead. It did, in my eyes, what those previous 3D adventures could not replicate. It was what the two New Super Mario Bros. games should have been.
Super Mario Galaxy 2, for me, is entirely deserving of the title "Super Mario Bros. 4" (or 5, I guess, since Super Mario World is number four.)
And Super Mario 3D seems like it's going to be more in that vain, so I'm thrilled.
I still like the Kart series, but the other sports titles are needless. Back in the N64 days, Mario Golf and Mario Tennis were the best golf and tennis games out there, that's not the case anymore.