Only Kingdom Hearts game to not have different difficulty levels for the player to choose from, something which it's remake Re:Chain of Memories would have.
In the Spanish version, due to translating and space problems, the general space for cards has an eye instead of a word.
Although Kingdom Hearts Final Mix was not released outside of Japan at the time, a number of elements introduced in that version are seen outside of Japan for the first time when this game was released. These elements not only include several special abilities and special attacks, but also the Neo-Shadow Heartless and the Diamond Dust and One-Winged Angel Keyblades.
Only Kingdom Hearts game where the fighting is done in a 2D environment instead of a 3D environment.
It's not explained why Sora bothers helping people out in the card worlds. They're not real so helping and not helping them wouldn't have consequences. Something that would be brought up in Coded, where Data-Roxas would tell Data-Sora the same concept.