Worst world is Pirates for me. Did not enjoy the gameplay of it at all.
Final "boss rush" battles where it's 2-3 Organization members at a time were meh. Would have preferred one on one, even if you didn't get to fight all of them. And how it goes into a cutscene if you beat one, then after the cutscene you still have the other. Like, what was the other doing during the cutscene, just twiddling his thumbs?
Did not expect Xigbar/Braig to be Luxu. I assumed he was connected to the Keyblade in some way from back in DDD, but did not expect it like that. I kind of thought he was more involved with Xehanort's plans than he let on, due to how cutscenes played out in DDD.
They did literally nothing with the box. It just sets up for the next story arc.
I'm not sure who Axel/Lea/AnsemTW/AnsemSoD were referring to when they said they experimented on a girl. Some people think it may be Ava (she's the only Foreteller missing at the end). Apparently there's some info in the Reports in the game, but I haven't gotten any.
I feel like they did a major step back on Aqua's character development. In BBS and 0.2, I get that she's a strong character, and is really composed. In KH3 I feel like she kind of just drew the short end of the stick a few times, and was a victim of time restraints.
I'm really salty they didn't do much with Larxene. Was hoping she'd get a lot more screentime. Was my favorite character in 0.2.
Axel finally got new clothing :D
Secret ending shows that Sora/Riku are in The World that Ends With You's world, I believe? I thought it was going to be Insomnia for a minute, I swear I heard Somnus playing.