My experience with KH3 went something like this:
1. After first playthrough: Utter bliss, felt like the game was totally perfect and satisfying
2. Starting reflecting on the plot and the way I felt after completing it. Began noticing that I was starting to feel a bit more negative about the game the more I thought about it. Certain things that had been built up to for years by previous games felt like they were resolved in the blink of an eye and not given enough of a chance to shine or breathe properly.
3. Have severe OCD, so it began to plague my mind thinking about all the flaws. Went online and saw the negativity and backlash, feelings have now gone from "utter bliss" to "mixed".
4. Went through a period of several months feeling very confused. On one hand, I felt REALLY great about KH3 and on the other, it felt like so much was missing from the experience in retrospect.
5. Replayed the game a few times, got platinum trophy. Opinion begins to feel less intense, and I settle on the fact that I would rate the game at about a high 7 or a low 8.
And now I'm here, which is that I feel good with KH3. I would say the only negative feelings that have persisted are similar to complaints you might hear in the Star Wars fandom, namely that Kingdom Hearts "doesn't feel the same anymore" as it once did. But, I believe a lot of that has to do with getting older. Kingdom Hearts has stayed relatively the same for all these years so I don't think it's the series that doesn't feel the same. I think it's the fact that I'm not the 2006 version of myself, and so I see things differently. I'm more critical/cynical than I was over a decade ago. So I'd chock that up more to my perspective of the series changing rather than the series itself "not feeling the same".
Besides, I didn't have that complaint immediately prior to KH3. That and, I remember feeling a similar way multiple times prior to KH3's release (such as when DDD released, and certain points with Chi and even 0.2). So it's nothing new. There's a certain "magic" that 2006-era Kingdom Hearts instilled in my heart that I always long to connect with. And most times, I feel it very strongly and it's my favorite thing about the series. Right now, I'm at a point where I don't feel it super strongly, but that's okay. No matter what, I will always have the magic and fond memories from 2006-era Kingdom Hearts within me. Nothing can ever take that away, even if I don't always feel it in the moment. And I'm content with that. Besides, I remember making peace with the fact that KH3 would never top KH2 for me about 2-3 years before the game released, and that turned out to be exactly the case and I'm cool with that. I just wanted KH3 to be a great game that satsfyingly ended the Xehanort Saga. And for the most part, that's exactly what I got. There were missteps for sure, but overall I think it was great.
So, Kingdom Hearts III is my second favorite game in the series, and I love it a lot. It disappointed me in some ways and it's definitely not everything I ever hoped for, but overall it was an incredible experience. I'd give it a solid 8/10 overall as it currently stands. Excited to see what ReMIND adds to it soon