>>718444182
Data battles are fun but you have to look for openings in all the bosses. I'd say in general KH2 handled them better with the openings but I digress.
Most of the new cutscenes exist for people who can't understand how the time travel works on the Xehanort side despite being covered decently enough in the base game, to explain some stuff at the Keyblade Graveyard including the "Namine recruited Lingering Will" thing from the JP-exclusive concert, or if you played KHUX. A lot of the new lines and scenes are for people who played KHUX, picture related being a very simple one.
The new Sora Scala stuff with Kairi is pretty great, especially if you like seeing them together.
Pro Code runs are pretty difficult with Lump of Horror, Skoll, and the Nort Court being the major hurdles with it.

It's worth the price for a Final Mix upgrade to the game if that's what you're asking, but most of it is backloaded to after you beat the game.