Things I love:
1. The characters. Sora is perfect here, Marluxia is mysteriously menacing, Axel is a snarky sarcastic douchebag and I love it, Jiminy is great, Donald and Goofy are wonderful as usual, and the Riku Replica is incredible always. Also, on Riku's side, Zexion had some enjoyable scenes, and Lexaeus is freaking great at being the stoic, dangerous powerhouse that we know him as
2. The gameplay. I love strategic games and melding in general, so the fact that I got both of it here made me very happy. We got an early form of command melding early on with the implementation of slates, and the strategy in the game (in my opinion) was wonderful. I know people don't like it because they don't like working for their prize, but I enjoyed it quite a bit.
3. The story. This is perfect as well. Easily on my top 2 stories.
If I had one major complaint, it's that Reverse/Rebirth's Disney world's were bland, boring, and generally unappealing. They were completely devoid of life and felt like they were made purely to extend Riku's gameplay since the developer's couldn't think of any clever way for him to interact with the other villains on Maleficent's council. Also, Riku's gameplay was way more boring than Sora's, and I don't understand why people consider it the superior version of the battle system.
Although I concede this point regarding Reverse Rebirth, it was still cool to be able to play as Riku/someone besides Sora and experience the CoM with new events and fight Org members we didn't get to fight as Sora. Other than that, I liked RR's gameplay, and I think Re: added more to it.