The game seems to have it's ups and downs. On the whole, I think I will quite enjoy it, as I have every Kingdom Hearts game. I doubt it'll be my favorite plot-wise, but it does do what it sets out to do: definitively end the whole Xehanort shenanigans. A lot of the character arcs end in a satisfactory way.
My favorite by far is the Days trio becoming the Twilight Town Seven with Roxas, Xion, Lea, Isa, Hayner, Pence, and Olette. I would honestly be happy with abandoning Riku, Kairi, and Sora and just having that bunch as the main protagonists next arc, but sadly I doubt it'll happen.
Definitely the best characters in the series.
The BBS trio fared alright as well, and Terra especially gets bonus points for how badass his return is. Aqua on the other hand got shafted hard, and I have to wonder why they even bothered with the Anti-Aqua subplot at all. Ven is just kind of there.
Kairi though definitely got the worst out of ANYONE in this game. Seriously, how did this happen? I say that, when it comes time to interview Nomura, we as a community make it our number one priority to ask him, why Kairi is only ever a damsel in distress and why he can't seem to write her better. Anyone with me on that?
Xehanort getting redeemed at the end I saw coming honestly. In this series, people can do terrible things to each other, but they are never definitively "evil". Just misguided. His motives actually make a lot of sense and resonate with me personally. I too sometimes think resetting the world would do good for the future. But the point that Sora makes is that Xehanort shouldn't have decided this on his own. Not should he have done all the terrible things he did in his eagerness. The message is that anyone has the potential to be redeemed. And the fact people wanted Xehanort to be killed ultra hard actually says more about those people than it does about the writing of his character. Food for thought.
Even with all of the bad that is in it, KH3 looks like a fun and amazing experience in and of itself. And I hope that we can get to the bottom of this Kairi bullcrap so that things turn out better next time. Sadly there's nothing we can do for people set on leaving after 3... I myself will still await the next installment.
I'm calling it now though: the epilogue will be about how Sora saves Kairi and what exactly happened to him, and that will start the building up to KH4. Meanwhile, the secret ending will reveal the Fortellers and "Her", who will end up bringing the Twilight Town squad directly back into the plot of the next arc. Next arc villain is the Master of Masters. Expect another one or two subtitled "side games" that take place between 3 and 4, but not as long of a gap as between 2 and 3. Those games will be a "Days 2" about finding "Her" with Roxas and Co., and a "Kairi finding Sora" game.