Kingdom Hearts games are always a beautiful kind of hot mess. The way they oscillate between Disney's enchanted kingdoms and the series' original labyrinthine realms–along with the infamously abstruse narrative–can leave even the most ardent fantasy enthusiasts bewildered. But for some reason, Kingdom Hearts 3 in particular is considered an exception, even a disappointment, among fans, even though all it does is bring the series's recurrent issues to the forefront, more overtly than any other Kingdom Hearts game.
The reality is that Kingdom Hearts 3 doesn't really do anything egregious to besmirch the name of the long-running franchise. Much like those before it, it takes its sweet time to weave a story that doesn’t crystallize until the very end (or until the developer decides to ret-con everything via spinoffs/DLC). The Disney worlds you explore feel more like whimsical jaunts rather than the main attraction, and the combat remains largely unchanged. It’s Kingdom Heartsy in every way, down to the last Pooh-nnoying detail.
As an avid Kingdom Hearts fan, I've learned to forgive the weirdness that often crops up in the series and instead appreciate what each entry does right. I am capable of turning a blind eye to Kingdom Hearts' convoluted jumble in Chain of Memories, for example, because of its innovative Yugioh-esque Action-Card system, and I willingly do the same for Dream Drop Distance's charming Pokemon-like Dream Eaters, as well as Birth By Sleep's highly customizable Command Styles.
That said, it's understandable why others might be so intolerant of Kingdom Hearts 3 in particular, as all it does is repackage the series' combat and adventure hallmarks into a more visually appealing and modern iteration, rather than tread new grounds or rebel against its own DNA (as 358/2 or Chain of Memories did in terms of gameplay and art style). Apparently, it's a sin these days if you don't burn the blueprint and start from scratch every time you make a game, or try to make it more streamlined for newcomers.
Despite Kingdom Hearts 2 being seen as the chef-d'oeuvre of the series, it actually had its own fair share of issues; cramped and confined locations, movement abilities tied to grinding drive forms, annoying reaction commands, and needless story padding forcing you to revisit each world twice. Kingdom Hearts 3 actually expanded on the worlds and made some of the movement abilities more accessible (in fact, now that I think about it, maybe grinding for these abilities in Kingdom Hearts 2 was what kept fans too preoccupied to notice the flaws).
Regardless, Kingdom Hearts 3’s expansions didn’t look or feel like the one-of-a-kind, free-flowing action experience that made the series so beloved, and the reason can be found in the success of some of its contemporaries. The last console generation had some dynamite action-JRPGs such as Nier Automata and Final Fantasy 15, which frankly blew Kingdom Hearts 3's combat out of the water. Combine that with the weight of nostalgia for its predecessor and a lot of expectation, and you have an uphill struggle to win fans over.
It’s easier to focus on Kingdom Hearts 3's flaws than to admit it’s just your average Kingdom Hearts experience, because the game itself isn’t really helping. I personally agree that the Gummi ship segments in Kingdom Hearts 3 felt like they had more depth to them than the story and the Disney worlds, and the big battle with Xehanort, which the series has been building up to since its inception, felt shallow and lacking in closure, but wasn't almost every other game in the Kingdom Hearts series like that? How many Kingdom Hearts games have asked more questions than they answered? Kingdom Hearts 2 does not even tell you who are you fighting against until you play 358/2 (released four years later), and there isn’t a single difference between the secret bosses in 2 (Lingering Will) and 3 (Yozora); both are bosses with no substance, just there as "please keep playing our games" gestures.
Also just like the Rewind DLC, which felt like a desperate attempt to fix Kingdom Hearts 3, half the games in the franchise have been repackaged and reworked several times in their final mix versions, with new bosses, and several cutscenes newly integrated into the main stories. Many Kingdom Hearts games were far from perfect on release. At least Kingdom Hearts 3 actually offered fresh and vibrant worlds like Frozen and Big Hero 6, and the story also moved the plot forward for a change instead of recycling the entire first game (yeah, looking at you, Recoded).
Kingdom Hearts 3 may not be the magnum opus that everyone has been waiting for, and it is a stretch to call it as memorable or unique as its predecessors, but to say that it derailed the series is a stretch. The only thing Kingdom Hearts 3 gets wrong is that it doesn't take into account how the games and fans have grown over the years, and stopped being patient with the series' weird story stables and other quirks, but Sora is still the happy-go-lucky and pure soul I grew up with, and that's what Kingdom Hearts is all about to me.