"Guardando nel Buio" features a sinister choir with a menacing recurring riff to show the crazy strength of this seeker of darkness who is on the verge of finally plunging Kingdom Hearts into darkness and the desperation of Sora who tries to stop him and find Donald and Goofy once more.
"Scherzo Di Notte", the battle theme for Hollow Bastion, is a chilling theme to show the desolation of the place, even with lots and lots of Heartless running amok.
Kairi has three theme songs and of the three, "Kairi III" is just... beautiful. Like music from heaven in its purest form... It's nostalgic, sad, and heartwarming. Kairi's other themes, "Kairi I" and "Kairi II" are just as beautiful.
The PLANITb Remixes of "Hikari" and "Simple and Clean" take the aforementioned songs and remix them into a different kind of awesome.
"Dearly Beloved" has made an appearance in every game in the series. It's the kind of music that takes all your worries away.
"Destati" and its variation "Dive into the Heart -Destati-", one of the first songs heard in the game. The music for "End of the World" is another mix of "Destati", complete with chimes, strings, and vague chanting in the background...or just vocalizations. There's a bit of vibraphone in there too. The effect is both beautiful and nightmare-inducing.
Destiny's Force is the theme used for very powerful bosses. It does its job at making the player feel like they're dealing with something powerful. The theme itself is also very intense, and uses its instruments very well.
"Another Side" plays in the Final Mix secret ending trailer, and it spawned "Organization XIII", "Graceful Assassin", and "Showdown at Hollow Bastion". A remix of the whole track was used in 358/2 Days, and the actual track was used in Aqua's battle against Braig in Birth By Sleep.
The many uses of classic Disney music during the game:
The "Mickey Mouse Club March" when we first visit Disney Castle is reminiscent of a king's army to show who's the one ruling there.
If you think that the first theme and second theme songs of Gummi Ship are light and happy, wait until you try to enter Hollow Bastion with your Gummi Ship. The third theme will blow you away.
"Hand in Hand", the Traverse Town battle theme, is a fun, frantic number to set the tone for all battles after this.
"The Deep End" plays during major boss fights such as Giant Ursula, Dragon Maleficent, and the first round against Ansem, laying out the insane strength of those bosses.
"Disappeared", the suitably creepy boss music to the Unknown in the Final Mix/1.5 Remix version, which pops up again in KHII as Xemnas's first boss battle theme.
"Night of Fate", very fitting for the night that kicks off Sora's adventure with the Heartless' invasion of Destiny Islands. It's also Traverse Town's first battle theme, before you meet Donald and Goofy. To add more epicness, try to listen to it when you're inside a room while there's a storm outside.