I've been trying to watch as many Hayao Miyazaki movies as I can recently. While they're all fantastic films, they do vary a bit in awesomeness and theme. I've seen most of them now, and I have to admit, Castle in the Sky is one of the best.
The movie is about a young girl named Sheeta. One night she's on an airship, and while aboard pirates break-in and try to steal her necklace. She climbs out the window and falls below, only to be saved by the magic inside the necklace's stone. A young boy named Pazu sees her float down to the ground, and manages to catch her and take care of the young lady until she wakes.
However the duo has little time to rest, as the pirates come to town to find Sheeta. During their escape they are also pursued by the army who also want to capture Sheeta and use the power of her stone to find Laputa. The land of Laputa is a legendary flying castle which allegedly holds not only valuable treasure by incredible power within. Which prompts many greedy people to abuse Sheeta's power and the magic stone.
I think Castle in the Sky combines the light-hearted theme of related films like Ponyo and Kiki's Delivery Service with the action of Nausicaä of the Valley of the Wind and Princess Mononoke. It features an impressive English voice cast (along with the Japanese audio if you wish), a compelling plot, and tells a wonderful story of mystery and magic. This is easily one of the best films I've seen all year long.