This review is based on the Disney version of the movie, voiced by James Van Der Beek, Anna Paquin, Cloris Leachman, Mark Hamill and others. The basic premise is extremely simple - it's the old good vs. evil, science vs. nature scenario, but the animation and imagination is so cool that it looks much more complicated than that.
In case you were wondering, this is not based on the book "Castle in the Air" by Diana Wynne Jones. "Castle in the Air" is the sequel to "Howl's Moving Castle", which was also done in anime by the master Miyazaki. "Castle in the Sky" has roots in the story of "Gulliver's Travels" where Swift wrote about a flying city named Laputa, upon which this film is based.
Sheeta is a young girl, now an orphan, who was given an amulet by her mother before she died. It seems that lots of people are after the amulet, and after Sheeta is taken aboard an airship by creepy Government agents, the ship is attacked by a family of pirates. During the fracas, Sheeta falls from the airship, and it becomes apparent that the amulet is much more than a nice piece of bling-bling. She is rescued by a young boy named Pazu, who is also an orphan and works as an assistant to a mining engineer.
Both the pirates and the army are going all-out to get their greedy hands on Sheeta, and we learn that she is a vital link to finding the mythical floating city of Laputa, which is said to be packed with both treasure and advanced technology, securely hidden within a huge storm cloud.
The main characters, other than Sheeta and the heroic Pazu are Colonel Muska, a secret agent with huge ambition, Dola, domineering matriarch of the Pirate clan, and the General, leader of the armed forces.
Although more than two hours long, this action-packed family movie is never boring, but it does contain some amount of violence.