Click to enlarge.

Now, from left to right starting with the first column. It lists the different story structure that the American version had (quicker), 100 tuning options to characters (bascially the tweaks they made for us for balance, etc.), English voice option, Arcade Mode, changes to the Duel Coliseum, and the ability for players to import their original Dissidia save.
However, of most interest are the three boxes of question marks below. The only particular thing I can think of at the moment are the moogle cutscenes, but there's obviously more to this than that. What changes await? We'll probably know at TGS next week.
SOURCES: Dissidia: Final Fantasy Universal Tuning - Official Japanese Site