Kingdom Hearts 2, released three years after the original, expands on the brilliant Kingdom Hearts concept (a young boy named Sora gains the power of a mysterious keyblade and must travel through Disney worlds to stop the evil Heartless from spreading) while polishing rough edges and expanding outwards with gusto.
Kingdom Hearts 3 might have fourteen years of dev time under its belt, but the second installment in the trilogy (excluding all the other games in the franchise, looking at you Re:Coded) is still superior.