As a lifelong fan of The Nightmare Before Christmas, I feel KH hasn't quite nailed it yet. I'm nitpicking at a lot of things here. KH1 certainly had the spookiness down, but visually it's off. More of a purple pastiche. The jack-o-lantern wall installations in the town square are too cutesy, almost like they were added for levity. KH2 was visually much more accurate to the movie, but I want more to explore. I wanna waltz through the whole town, cemetery, and hinterlands, see inside town hall and Jack's house. I don't even need Christmas.
They haven't fully realized the potential of Oogie's blacklit neon torture casino. We still haven't seen him green! There could be a full winding dungeon beneath the town (expanded, as the treehouse was in KH1), or the aesthetic could bubble up and take over the town itself, along with swarms of creepy-crawly Heartless. Oogie is also literally the Boogieman, a very fitting symbol for a series about the darkness that lurks in the heart. He's also just a bunch of bugs in the end, a visual metaphor not unlike the ant-like Shadows.
Another important thing to me is the field theme. It doesn't need to be This Is Halloween, and shouldn't be. The everyday mood in Halloween Town is more melancholy and eerie. It's not a thumping celebration all the time. Sally's Song is a more appropriate leitmotif for the town, but something original by Shimomura that matches the mood of the score would be just as welcome. A jazzy theme just for Oogie's lair would be excellent.
Seeing more of the bizarre residents of the town would be nice. I would like to see the clown tear off his face, then reach inside for an item. If there was ever a movie to devote extra attention to the NPCs, it's this one. Frankly, it's the best Disney property KH has to work with. Even the Heartless feel at home in Halloween Town. At this point, they have the technology to realize the town as it was in the movie, exactly. What an insane privilege that would be. Halloween Town (and Wonderland) should be a series mainstay. It complements the psychedelia of the original worlds perfectly, and is a more "humble gothic" so it wouldn't necessitate not also including a grand gothic castle world, even if they're both spookyworlds. It would also be nice to see the town during the day (especially at sunrise), or even covered in snow!
The developers not being able to think up a good story for the world is no excuse, as that has not stopped them before. Nomura said this is one of his favorite worlds, so here's hoping it makes a comeback, better than ever.
Also. Jack, as a curious cat who delights in the exotic, should get the chance to travel through the barrier to see other worlds. Screw the world order.