I think some of KH2's worlds were the best in the series, because they took the concept from KH1 and just tried to make them more interesting-- back when the series was still about "hey, crazy Disney worlds!" rather than "ORGANIZATION NOBODYDREAMEATERXBURADO" insanity. Not all of them were great, but I think in more recent entries (ESPECIALLY 3DS) it's clear that they're focusing less on exploration or meaningful interactions with the Disney worlds and more on "how insane can we make this combat?" which I think removes much of the impact and enjoyment of discovering new worlds and seeing new characters.
When things have become so over-the-top, there's no grounding anywhere to make anything meaningful. In KH2, it felt meaningful when you unlocked double jumps, superglides, and all the air dashes because the system didn't go from 0 to 60 like DDD.
That said, I think there are good bits and pieces in many of the games (heck, even some of the weird minigames in re:coded were entertaining) that, if they can manage to combine them all meaningfully, will make for the best game in the series.
Get the grounding and emotional weight behind some of the earlier games (and BbS), the satsifying ability progression from BbS, the crazy changeups from re:coded (shooters, turn-based stuff!), the world visual design from DDD, and some of the level design from KH2, and I think we'll be good to go.
And as I said before, make Donald and Goofy a meaningful part of the story again. I like their friendship with Sora far more than Riku's.
Also Star Wars and Avengers worlds plz
ALso, again, I'd really like to see more immersive DIsney worlds. I don't even care if there are FEWER Disney worlds if the four or five that there are are more meaningful. The nature of the 'explore the worlds in whatever order' thing they've had going on, along with the "okay here's a DIsney interlude with OXIII members plotting somewhere else for the real scene at Hollow Bastion after you finish three of these" needs to end. Cohesive narrative!
Okay so yeah I just have a million suggestions for how to improve thins.