A bad game, in all honesty.
I enjoy every KH title and this one is not even that low on my list as my words might suggest, but being objective it has very little going for it.
A lot of bad ideas, or poorly implemented: and most cool facts were so hidden they might as well not being there (seriously, how were we supposed to guess Master Xehanort possessing Young, Nomura? And that he was using No Name with a different keyholder? It's cool and I love it, but it almost only truly exist in the pages of your interview)
Dream Eaters and Sora are constantly competing in my mind for what I hated the most.
Let's throw a bunch of good points, why not.
I'll say, while I disliked almost every Keyblade design, Unbound was conceptually neat, and End of Pain legit good (then again it wasn't made in the style of the other ones).
Also I like how they're implemented: having one for completing Dives, Flick Rush, Portals and such was a neat concept. You finally felt rewarded for something other than a high level or mashing X or Triangle.
And, albeit only at the end, you could modify how your weapon looked and even "roleplay" a bit (Sora with End of Pain? Riku with Divewing? And what's the headcanon for these choices?)
What else... Ansem's new transformation LOOKED cool, I guess?
Oh, right. Simphony of Sorcery. Easily one of the best worlds ever, that managed to win over even the game's most implacable detractors.
Or, like my brother named it, "finally a world without hearing those stupid grunts".
Personally, I liked the flashbacks and chronicles, mainly because I just love the feeling of getting something new and going through it (I spend a lot of time checking off the "NEW!" signs in the Journals).
For similar reasons, I liked getting a cutscene after finishing every world.
Kingdom Hearts Dream Drop Distance is a mixed bag... with a 1:8 ratio of good and bad. The true embodiment of the life lesson that you can totally enjoy bad things as well.