Spoilers for the entire game, including the optional reports. You have been warned.
First I want to talk about the positives, since it's only fair to do so. The party banter between Sora, Donald and Goofy has never been better, and this for the most part extends to their dialogue with Disney characters. They're also very expressive in their body movement and the camerawork during cutscenes is also the best in the series so far. The game is also very funny, I laughed out loud several times in almost every world, and especially the self-aware humor is highly appreciated (KH II.9, Jiminy giving everyone plot summaries, "Don't you know how popular I am?" etc.). Individual scenes could hardly be better, the problem I have with KH3 is with the overall structure that ties them all together.
The game even starts off good, really good. Olympus and Twilight Town contribute well to the story, as the gang has legitimate reasons to go to those worlds. I was especially pleased with Sora having actual emotion about having lost his powers when playing through Olympus. In regards to Twilight Town, it's a shame that the setup for using the digital Twilight Town for bringing back Roxas isn't used in the story itself, but is just tucked away into an optional report as a handwave for why he could come to Keyblade Graveyard on his own. Still, at least it didn't feel like I was wasting my time.
After that, the story comes to a screeching halt for the next 15 hours as you explore random Disney worlds and accomplish nothing. Sora is supposed to be looking for "the power of waking" but does nothing to that end, and then the plot just gives it to him after it's done with the filler. No, outside of Olympus, Disney worlds don't contribute to the story at all, even in KH3. Toy Box and San Fransokyo at least foreshadow the the replica-thing, but nothing is really accomplished. I guess Monster's Inc. world explains why Vanitas is back but it makes little sense, though I can appreciate trying to tie it to the overall plot. The unfortunate thing is that these are isolated scenes and instances for lengthy worlds where SDG have little to no reason to be in. They're just filler. All the plot happens elsewhere, so let's talk about elsewhere.
There is some nice setup for Roxas's return with Vexen, Ansem and Ienzo, but too bad the final resolution of that is in an optional report, so it still feels like he just falls out of the sky. At least they tried with him ( looking at you, Xion ). Riku and Mickey go to Dark World, then realize Sora still needs to go through 15 hours of filler, so they leave, do nothing, get some new keyblades so that SE can sell more merch, and then go back to Dark World and the plot resumes. There is extensive setup for a mystery test subject girl that Lea and Isa were trying to save. Wow, can't wait to find out what that is all about! There is some setup for an extra purpose for Demyx/Luxord/Larxene/Marluxia. Wow, can't wait to find out what that is all about! Maleficient and Pete are looking for the Black Box from Back Cover. Wow, can't wait to- You get the idea.
Kingdom Hearts 3's main problem is that it lacks an identity. It lacks a story of its own. Everything it does is either filler or setup for future games (or DLC), until you get to the endgame.
Aqua and Ventus are saved, but it's payoff for a setup in another game. Sora and Kairi share a Paopu fruit, but it's payoff for setup in another game. Lingering Will saves the gang, but it's payoff for setup in another game. Riku Replica sacrifices himself to help Namine, but's it's payoff for setup in another game. Sea Salt Trio reunites, but it's payoff for setup in another game. No, I'm going through each one this time. Terra breaks free and saves Aqua and Ven, but it's payoff for setup in another game. All the villains have death monologues, but they're payoffs for setups in other games. Sora beats Xehanort with barely even knowing who he is, because it's payoff for setup in other games. Eraqus has a reunion with Wayfinder trio, but it's payoff for setup in another game. We get happy reunion scenes and they're all payoffs for setups in other games. The end.
I get it, it's a sequel, it's a finale, but it has to tell its own story. This is the absolute bare minimum KH3 could possibly have been. It's throwing isolated sad scenes at us, with absolutely nothing else going for it. And even these scenes barely contribute to the plot. It's ticking off a gigantic checklist. Of course the game had to have these things (most of them anyway), but it needs to do something of its own to be a good story, worthy of standing beside the ones it ended up just leaning on.
Now, I have to recognize that KH3 isn't at fault here. Kingdom Hearts 3 is a victim of its own series. The game has to majorly consist of Disney worlds, but the writers can't tie them into the plot, so most of the time is wasted. The game has to resolve the stories of half dozen spin-off games, so they're all crammed together with all the characters getting barely any screentime outside of those. It's even cannibalized by its own inevitable sequel, because everything original KH3 does, is setup for that sequel. The game is being pulled in far too many directions because this series has become too expansive for its own good. The 13 years of story-relevant spin-off games has finally come around to bite them in the ass. It's a good thing we're finally over with Xehanort Saga so that the story can move on without all this baggage.
Perhaps the character that got the biggest shaft here was Kairi. She's in hyperbolic time chamber doing off-screen training for the whole game and has like two scenes with Sora. Then we see the fruits of this all training, she's elevated from being helpless to... still being helpless. Like... I don't know if this is some kind of super meta joke again, but c'mon, she gets kidnapped for a third time. And then she just fucking dies and everyone just forgets about it until the end, where she is revived off-screen just to create another sequel setup with Sora vanishing.
To be clear, I don't hate the story of KH3, I enjoyed all the callbacks, but it's just incredibly disappointing that that is all there is to KH3. Before release, everyone was adamant about players needing to have played the other games to understand the story and feel the emotional impact of KH3. I guess we were half right, you need to have played the other games to feel the emotional impact, but you don't need them to understand the story, because there is no story.