Liked:
Panel System - Actually, I pretty much adored the panel system. One of my greatest loves is customization and the panel system gave it to us in heaps. I swear I spent more time tweaking and testing my panels then I did in actual missions.
Backstory on Axel and Roxas - Frankly I think this was REALLY needed. It helped me buy how Axel went from badass assassin in Re:COM to "MUST SAVE ROXAS!1!11!" in KH II.
Story - I liked how instead of epic, the game focused more on day-to-day interactions. It really allowed you to connect with the main characters.
Organization XIII - Yeah, they could have had more emphasis on some, especially the CO members, but still, anything is better than nothing. And Xigbar, Saix and, of course, Axel, got some pretty decent development.
Music - I LOVED the music in this thing. Especially Xion's theme. All the ending cutscenes were made about 50 times more powerful by the amazing score behind them.
Mission Mode - Who DOESN'T want to play as Org. XIII??
Disliked:
HP of certain enemies - This just got ridiculous at times. If you want to up difficulty, improve AI don't just pile on the HP bars. >_<
Story - This isn't really a legit dislike, but man. Can you say DEPRESSING?? Good grief.
Mission Mode - Some characters just stink *coughXEMNAScough* no matter what you do.
Overall, I loved the game. It really surprised me, especially for a DS game.