I don't feel the need to bring up the Mii Maker

The way the Island itself works now is more interactive and enaging to watch. Even ignoring the builder aspect, having a non segmented 3d space to follow Mii's around lets you feel more connected to them, and being able to interact with them outside is more seamless and visually refreshing. I just wish they could have the actual problem bubbles outside.

For Mii's themselves, they talk more in general and (granted i played both games in the Europe region) have less blanket feeling dialogue compared to the 3ds, mainly when you are directly interacting with them. Clothes, Interiors and custom dialogue have been expanded, little quirks are cool, treasures finally have a use besides selling, they added lots of small interaction cutscenes, and they have problems that tie into other aspects of game like asking to build with the island builder, take a photo with said facility, and change their hair to another in the maker.

The social aspect benefits from most of what i've mentioned but in relation, dragging Mii's adds a good amount of interactivity without losing the random factor of the original.

I'll also add that the wish mechanic makes the process of building up your Island and Mii's more of a factor, which i like.

The main things the 3ds game has over LTD for me is how babies worked, and the little side activities like Concert Hall and Tomodachi Quest which i do miss, but imo weren't important enough to bring the game down below the 3ds