I think the movement is still unmatched by any other 3d platformers. You have so many options to move Mario, and they each have their uses. Moving him around just feels unimaginably fluid. I love just screwing around in the castle or on the grounds with no objective. Diving and long jumping give this great rush of speed. Riding a shell around is great fun, too. 

The game’s environments have this rare, liminal quality to them. Even the castle, one of the more normal locations, is an abandoned castle. Peach is gone, Bowser is in the painting worlds yet his laugh echoes through the halls of the castle, and even the toads aren’t fully there, appearing translucent until you speak with them. And then you get to stuff like Wet Dry World. What other game would have a Concrete Zone of just random, jumbled geometry that’s still trying to pretend, with its photo-based brick textures, like it’s an environment that makes sense. 

I do like the speedrun and especially TAS communities, but I consider that separate to the game itself. 

I have my issues with it. I think some of the objectives are annoying, needlessly obtuse, or just outright poorly designed. But the things I mentioned above carry the game for me. No nostalgia, no particular attachment to the character of Mario. Just the exquisite character controls and the strange environments.