As someone who's playing both NL and NH right now, NH is definitely the superior game in my opinion. I have so much loving nostalgia for NL too. Horizons looks incredible and there's so much more to do in general on a day to day basis. (terraforming, island hopping, decorating, etc) I can play NH for a few hours a day where NL I run out of stuff to do after about 15-20 minutes. NL definitely beats NH in terms of dialogue, extra content, and general life in the game though.
NH was neglected for sure, and that's the number 1 problem with it. There was a ton of QoL updates they needed to make to the game. They got more than they wanted out of the game and therefore abandoned it years before it should've been abandoned. I say this all the time, but they needed to add perfect fruits and all the island fruits missing from NL. Perfect fruits have been a special staple in every AC game. (perfect apples and cherries were so beautiful and I miss them dearly)
And as for the island fruits, how are you gonna have an AC game specifically set on an island and not add persimmons/durians/bananas/etc that were in New Leaf?? It still blows my mind to this day that the game lacks these super simple features that'd cost them nothing to add.
I have the same problem with the shop. Nook's Cranny only got one upgrade when I believe Nook's Emporium was the fourth or fifth upgrade? Gracie is nonexistant as well. I believe they were going to add all of these things eventually but for some reason just didn't.
NL got a huge update after what, 5 years? I was hoping that NH would get a big final update around this time too before the next game is announced. As for the next game, they already have all of the villagers modeled and I don't see how they can make the graphics any better than they are now, so I hope more resources go towards dialogue, decorating elements, and character customization cause that was also pretty lacking in NH.
I apologize for being all over the place, I have so many opinions about NH but it's definitely far from being a horrible game. It's just disappointing that they abandoned it so quickly because it had so much potential if they just kept up with it. I'm hoping the next game will be a combination of NL, NH, and PC because Pocket Camp was fantastic for what it was. I want a focus on character customization and furniture next game.
These are all just my opinions. I tend to say stuff over and over though so apologies for that lol