Incoming Wall of Text: Copy-pasting and adding to my post from
another thread because it is a detailed opinion of the game:
Things that I love: It strikes a good balance between creative and restrictive play. While ultimately I can design any kind of environment that I can imagine, at first I am constrained by lack of resources. But instead of cramping my "vision," I am forced to either come to a creative compromise using what I have (which often leads me to whole new avenues of inspiration) or I can admit defeat and abandon the client. I can also do a passable, bare minimum interior and revisit the project once I have the items that I think would really "make" the home. And at no point am I punished for these choices.
Another thing I love about the game is the resolute eccentricity of some of the design demands. It injects the game with a ton of personality and reveals a sly sense of humor that I think was missing from ACNL. To date, I've handled requests for everything from spa retreats, bowling alleys, and pizza parlors to more nebulous concepts like "the land of the free" and a "place that is all about wood." Personality is revealed through things other than dialog- it is reflected in the types of spaces that villagers request, and even similar sounding requests reveal very different "takes" on the theme, based on the resources that are unlocked.
The item-villager interactivity adds some much needed dimension to the somewhat diluted ACNL personalities. I love that villagers cook when you put a stove in their house, or bust out a tambourine when they listen to music. The ability to clothe and accessorize them adds even more customization and expression.
The mechanics of decorating are more fluid, and make better use of the DS. The ability to customize windows, doors and the addition of ceiling decor makes interior design even more rewarding and challenging. Again though, if you're not keen on decorating, these points will not change your mind. The implementation of Play Coins is also more useful than it was in ACNL. Overall I think HHD integrates the DS's capabilities and features quite well.
I've also noticed that my affection for a wider range of villagers has increased in HHD. Instead of seeing the 400+ cast of villagers through a boring, binary lens of "dreamy" or "tier rock bottom" I find myself anticipating a wide range of characters, in hopes of uncovering more unique design requests. Also any villager might be the one to unlock an item that I will love using, so that encourages diversity in my client selection.
Things I don't love: I think that the dialogue could have been less general and more reflective of the specific features of what you built. And yeah, after decorating so many great houses, and with so many new design elements, it would have been hella sweet to go home and decorate my own house!
Hopefully since they are using telemetry this time around, they will take note of the various features and how they are succeeding/failing, and fine tune them for the next installation.
Ultimately I think the success or failure of the game will depend on 1) how realistic you are about your expectations of a spinoff, and 2) which qualities of the parent title you valued most and how OK you will be with the absence/modification of those qualities in a spinoff. I've been playing AC titles since the Gamecube, and I greatly enjoy HHD as a spinoff that capitalizes on the creative features of the franchise while mostly ignoring the more Sims-like elements.