I gave my HHD code to my brother and the download finished last night and he's been playing it non-stop. These are the things he told me.
1. Character creation is much different than before. You do not get asked questions that determine your appearance. You have a new menu where you personally select the face, hair, and skin tone of your character. If you couldn't tell, you couldn't change your skin tone before. This is a feature I want the new AC game to keep.
2. Amiibo cards are not only used to summon characters early (it's slightly random who'll be your client that day, sometimes it's pre determined to teach you something) but they are used to change the positions of the employees who work at the building such as the School, Hospital, and such. When you make a new building, characters are randomly assigned to the positions. You can't choose who gets what spot. And you can't change them unless you have the cards. They are also the only way to design houses for "special characters" such as Isabelle, Reese, and DJ K.K. who disappear permanently after their introduction unless you get their card. Gee, thanks Nintendo.
3. The house designing part is the best part because there's a lot more to do to it, but it is the game's major selling point.
4. You do not get to roam a town, only the outside of Nook's Homes, where you find new clients for that day. Very dull if you ask me.
5. You are forced to wear the red blazer when you're doing your job, you can visit the villagers and buildings you've already made with any outfit you unlock.
6. Doing jobs for certain villagers unlocks certain items, clothes, and furniture for you to use now and later.
Aside from some improvements, this game is mostly not a sequel to New Leaf, more of a spin off for hardcore fans. It doesn't sound interesting to me.