KH1 and KH2 were a shared, magical experience between my older brother and myself and I have very fond memories of these games. I just played through 3 but I feel like I'm missing so much of the story. I didn't realize that the other miscellaneous games outside of KH1/KH2 were considered cannon to the series, so I have no idea who the heck Aqua or Terra actually are.
Another complaint is that I felt like the game ended abruptly as well, as the 'final boss' battle felt pretty.. low budget. I expected amazing animations or cinematics during this fight and it didn't really pan out that way.
There are also some sections of the game such as the 'Frozen' world where your only real interaction with the characters of that world is to.. rebuild Olaf..? Elsa completely blows you off, and you see Anna, Kristoff and Sven for just a few short moments. Really felt like they could have done more to include Sora in the story rather that just re-creating exact scenes from the movie. The Pirates of the Caribbean part felt similarly unengaging/lack of original depth.
Overall I'd recommend it only if you've played the other games in the franchise, or if the game goes on a decent sale.