BbS is objectively a flawed game with a poorly designed gameplay in which a character, a really floaty character with opposite of fluid movements, has to completely stop the action he's been doing before you can give it another imput; with bosses with random blocks/counters/attacks/desperation moves that abuses things such as invicibility frames to give you the good old fake difficulty feeling.
You have to use a certain tactic against some secret bosses, and you 100% cannot just attack them in another way because that will just not work. And a game that forces you to do only a determined set of actions when you theorically have more is at fault.
Oh, and... they clearly forgot Terra was a character while designing most secret bosses. Up until now, most Terra tacticts still include "and you have to be lucky" at the end of the strategy.
Some people find this a fun game where you have to "guess" what kind of command will make you instawin the fight, and more power to them, but this still penalyzes those who wanted to win using their favourite skill, which KH II allowed to do.
Commands are cool, they would've been much better if most were useful and balanced, but the game frontloads you with a lot of stuff that is either useless or not as effective as purported to be most of the times.
Story has its flaws, but it's a gigantic topic on its own where personal tastes are even more relevant. I'll just quote things like the unnecessary Donald and Goofy cameo that confuses fans up to this day and Kairi's "ceremony" to show it can be silly.
All of this is not to say BbS is straight up shit, or that one should not like it (it's still my 2nd fave KH title), but then again is not just "different". It's plenty flawed.