I dislike Reaction Commands as they were executed in KH2. I like them in Birth by Sleep however. So I want more of BBS than KH2 when it comes to reaction commands, because it was insulting to me to initiate a 'reaction command', especially at 'forced situations' such as the Twilight Thorn.
It was a love/hate relationship with me for the reaction command difference between KH2 and BBS. On the one hand, I liked KH2's because it was only
one button that I would have to push all the time, so I didn't have to worry about pressing the wrong button, just getting the timing right (unless I was dueling a Samurai or fighting Luxord or one of his Gambler Nobodies), on the other hand I disliked it because it was
only one button in most cases. In BBS though, the 'press X to not die' segments were very well done, except for THAT ONE QUICK-TIME EVENT against Vanitas as Ven where freaking
everybody disjointed their thumbs and feared they'd break their PSP rolling that stupid analog stick around in a circle as fast as humanly possible or as fast as they feasibly could in whatever situation they were in which might have caused that event to go on for a minute until you or Vanitas finally won that one. Seriously, that one was TORTURE!!!
The one thing that I'd rather they go back to though instead of following through on BBS' example was KH1 and KH2's expanded magic system. I get that synthesizing and leveling up your different spells and creating new spells and abilities is cool and everything, but I preferred some of those abilities happening automatically when you equipped them like Explosion or Slide Dash or Aerial Dive, because it really felt like Sora was growing more powerful as he leveled. In BBS, if you didn't synthesize anything (which would be against your best interests), you could end up going through the whole game using the Deck Commands Fire, Slide Dash, and Quick Blitz, and while that might work for you, I have to remember that these guys are essentially Keyblade Masters and Sora's still only had his Keyblade for a year and he's already surpassed them in style points.
The other thing was magic and item usage. I didn't like that in BBS I would have to give up one of my physical attack deck commands if I wanted to use magic or have a potion ready for emergencies, rather than having the magic/item hotkey system. Then again, in BBS we didn't have L1/R1/L2/R2, so there weren't enough buttons for it so the command system had to suffice, but I'd really rather have my magic bar back and my ability to cast Reflega, then charge into the fray and do some damage with the Oathkeeper to any that survived the magical backlash the Heartless got for attacking me while I had my Reflega shield up, then cast Magnega followed by a few Thundagas and then hitting Reflega again before quaffing down an Ether and I can mix up the whole thing spontaneously without having to worry about reload times unless I've run out of mana.