My favorite game. Of all time.
First I'm going to start with the story. It begins as a boy named Sora is on his home Destiny Islands, and with his two best friends Riku and Kairi. And on this island there are also Final Fantasy characters: Tidus, Selphie, and Wakka. Suddenly the world has been connected to darkness and is destroyed by beings called Heartless. Sora teams up with Donald Duck and Goofy from Disney with Jiminy Cricket providing a nice little documentation of your journey for future referance, after arriving at a refugee like town, where he meets several Final Fantasy characters as well: Leon, Yuffie, and Aerith. Leon tells him that his "keyblade" is the weapon that can destroy the Heartless, AND release the hearts. Aerith tells you that Ansem, a man from their old world experimented with the darkness and created the Heartless, and that Sora should go looking for Ansem's Reports which provide very helpful insight into understand the game better. So once they leave Traverse Town, they have to go on a quest to seal the keyholes from other worlds to prevent Heartless from destroying them. The game takes you to several Disney worlds such as: Alice in Wonderland (Wonderland), Hercules [Olympus Coliseum] (which is where you meet Cloud Strife by the way), Tarzan (Deep Jungle), Aladdin (Agrabah), Pinocchio (Monstro the whale, yeah he swallows you), Nightmare Before Christmas (Halloween Town without the Christmas parts), Peter Pan (Neverland), The Little Mermaid (Atlantica), Winnie the Pooh (book you go inside in Traverse Town), and a few Kingdom Hearts related worlds.
Next is gameplay. The gameplay is fun and I love it. It's very easy to get the hang of, but there's one problem: The camera isn't very good. You can lock onto enemies with R1 on your DualShock2 controller. There are four commands to choose from, Attack, Magic, Items, and the fourth one is used for activating combos, talking to people, and opening chests. There's also a short-cut menu which you can set items and spells to for quicker use, when your in the heat of battle. As you progress through the game, you get keychains, which you can attach to your basic keyblade (Kingdom Key), and it changes it into a more powerful keyblade. There are abilities, such as dodge roll and glide or block. The bosses are challenging, and fun, and your find yourself losing so much one battle, by time you beat said battle, you can memorize the entire cutscene.
Soundtrack and Voice Acting. Great voice acting, from Final Fantasy characters, Disney characters, and famous actors for the various voices. Sora is voiced by Haley Joel Osment, who I might add does a great job, as your spiky-haired giant key wielding protagonist. The music in this game is amazing, although not composed by Final Fantasy's legendary composer Nobuo Uematsu, Yoko Shimomura does an incredible job, with wonderful tracks, that you'll find yourself humming to, in absolutely no time at all.
Replay Value. A lot. I've played this game over and over again. It's really worth a replay.
Overall: Great game, incredible story, amazing music and soundtrack, and replay value is incredibly high. 10 out of 10.