Having beaten the game I am sort of indifferent about it. Its not bad, a very fun single player game in fact. But I think the other numbered KH games are better. Even 1, though obviously not in terms of raw gameplay. BBS too, but its essentially 0 (I grew to like BBS a lot when it hit consoles).
There aren't many worlds, but seeing their size it makes sense why. However, they don't push the story forward at all. During the first hour of Pirates I fell asleep, there was barely any gameplay. I have to rewatch those few cutscenes soon because this wasn't a joke. I think the game misses some KH worlds, like Radiant Garden, Scala, a proper Twilight Town or even Traverse Town.
The worlds are hit and miss. Olympus was great. Toy Box was meh with too much mech stuff going on and I didn't like the mall much. Tangled was great. Frozen was wtf is this about (its not good). BH6 was good, Monstropolis was good, Pirates was good in scale but if I look back all I did was collect crabs to power up, do a few ship battles and fight the boss. And watch a string of bad cutscenes going nowhere. There isn't much reason to go back to any world with newly acquired skills, the wallrun is sort of deus ex machina and cheap tbh.
Then it funnels you through the story, which is cutscene -> battle cutscene until the credits. Thats fine and dandy but as much as the other players I had legit questions about the character building and usefulness of Kairi and Lea for example. And Xehanorts motive? I don't know.
As for the gameplay, I was deliberately avoiding attractions and Links because its boring, easy and automated. This could use a rebalance. I wasn't too hot on keyblade transformations either but its personal, I have used the Kingdom Key throughout the game. Good thing you can upgrade them to keep them relevant. Perhaps KH2 FM was a fluke, because that gameplay hasn't been rivaled by any other entry.