Many of the Entries of KH games after 2 feel like Assassin's Creed level of "Spin off but A sequel but not". Those games wore the continuity out way too thin. And the a few elements they did add in are so boisterously convoluted they muddle the experience of KH3 once we finally got there. I am not alone in saying KH3 was a massive disappointment in the story department mostly due to the plot threads added in from all those portable titles. My company's stores have massive amounts of trade ins with most people reflecting some level of dissatisfaction with the game.
Spin Off or not, the bouncing between different platforms greatly hampered gamer's ability to keep up with what was happening in the story, and releasing mega collections for the PS3/4 only partially remedied that because the threads just don't come together neatly at all.
The lack of FF characters in KH3 really was the killing blow for me. I got into the series for the FF, not the Disney. Albeit I will say the Disney element is as solid as ever in KH3. The omission of so many staples to the MAIN series like the Colesium and Sephiroth battle just really frustrates me. You might subscribe to Nomura's excuse of "focus", but I have the strong hunch we will see some of this appear as paid DLC and that is just criminal when KH3 has decidedly less content then previous entries, even the handheld ones.
PSN:Forevercloud (looking for Soul Sacrifice Partners!!!)