Great story, better controls, sweet graphic and assist characters that kick ass to boot! What more can you ask for??
One major plus in this game are the extra playable characters in every different world... at last they actually made them appealing enough for us to actually use them in the game! Those combo attacks customed to everyone of them really was a pleasant surprise! I remember that in KH1, I would never use the sub-characters as they just would play well and I couldn't open any trinity marks without Donald or Goofy.
Also, the storyline of this sequel was more than I expected! Actually making all the connections from KH1, the development of Riku's story, The King being a major part in all this... just awesome! One little disapointment: Final Fantasy characters had very simple roles compared to all the Disney ones....
In any case, can't wait for KH3!