It's always sad to see a particular style you loved go, but as it has come up a few times, I'm glad Nintendo kept changing it up with 3D Mario. Introduce the concept. Evolve the concept. Try something totally new.
It's not unlike how they handle mechanics in the actual games themselves, never hanging onto something long enough for it to stagnate, or prevent trying new things.
If there's one constant for Mario, it's this. The little dude started off in a King Kong spoof, moved to a co-op multiplayer game, then hit gold with a platformer... before (in the US) being in a weird vegetable game, followed by two more traditional platformers, then a weird Yoshi game, then a sea change to 3D exploration/adventure.
Change is at the heart of Mario, and why it's persisted so long. You kind of have to. No matter how good it is, no matter how much you improve it, you can't keep making the same game over and over again. Entertainment is a large part about surprise and discovery, and that gets impossible after a certain amount of time.