Kingdom Hearts is a PlayStation 2 game made by Squaresoft and is comprised of Disney and Final Fantasy characters. It's an action-oriented RPG. The beginning of the story is simple, the Heartless are taking over worlds, and you (Sora) with Donald and Goofy have to find King Micky and set things straight. However, don't turn it down simply because of the Disney influence, it's a fantastic RPG guaranteed to give you at least thirty hours of solid gameplay, and there are many things to do after you've beaten the game. The FF cameos present are: Moogle (Various), Yuffie (VII), Cid (VII), Cloud (VII), Aerith (VII), Squall/Leon (VIII), Sephiroth (VII), Wakka (X), Selphie (VIII) and Tidus (X). Although I might've missed one or two.

Although I've never played Xenogears or Radical Dreamers so I can't help you on those two.