Differences
"Kingdom Hearts II: Final Mix" features more bosses, mini-games and dungeons than the original game. "Final Mix" also has new cutscenes, which extend the storyline. In addition, the difficulty level called "Critical Mode" is only available in the "Final Mix" version.
Considerations
The dialogue in "Kingdom Hearts 2: Final Mix" is dubbed in English; however the text is in Japanese. The game will only work on consoles imported from Japan, or American consoles modified to play foreign games.
Fun Fact
When released in Japan, the game's package included "Kingdom Hearts Re: Chain of Memories." This was a PlayStation 2 remake of a Game Boy Advance game.