I've seen this movie more than three times and it's pretty enjoyable.  I wasn't bored watching it multiple times, like I often do.  The story is imaginative and creatice and the story reminds me of Atlantis by Disney, which probably was inspired by Castle in the Sky.  I think I've also seen this anime under the name of "Laputa", which is the name of the castle in the sky in the story.  I like most, if not all, of Miyazaki's anime, and this is one of them.   

Pazu, a mining apprentice, finds Sheeta, a younger girl, floating down from the sky with what seems to be a glowing crystal pendant that she wears around her neck.  There are two groups of people, pirates and the government, after the magical crystal and Sheeta is in danger. Together, they find that they both are seeking to find the legendary floating castle, Laputa, each with their own reasons. Pazu, along with the help of miners, tries to safe Sheeta from the pirates and the government.  With the twists and turns of the story, Pazu, Sheeta and the pirates lead by Dola, teams up against the true villain of the story, asecret agent, who happens to be a decendent of Laputa, also.