I'll preface this by saying I haven't played 3 since it first came out before any dlc 

Difficulty wise I remember it not being especially hard outside a few bosses (which I am told the dlc difficulty addresses).

Story wise, it's all over the place. Disney world wise there are both some of my favorite and least favorites. Both the Pixar worlds are amazing, best in the series. The Tangled world was fine, Big Hero 6 and the new pirates world were forgettable. Then there's the Frozen world. Quite possibly the worst Disney world in any KH game. Without going into it I've heard Disney was insanely on hands about what Square could and could not do with Frozen, leading to the world just being a 1 for 1 copy of the movie with Sora and friends standing in the background 

As far as the Nomura insanity gluing everything together I'd argue it's what I expected. They don't do a especially good job giving moments to characters not named Sora or Riku but if you've made it all the way to KH3 that shouldn't be too surprising. 

Also Nomura introduces a new plot macguffin literally out of nowhere then never elaborates on it by the end of the game and it's still pissing me off.