Stardust is a fun, beguiling, and often unpredictable fairy-tale.
Reviewers are comparing Stardust to Princess Bride (but without the quotable one-liners like "As you wish" and "I am Inigo Montoya. You keeled my father. Prepare to die!"), so I'll be different. I'd say it's one part Willow, with the innocent that needs protecting; one part Harry Potter, with a not-quite-seamless blending of magical and mundane worlds; and a tiny bit of Pirates of the Caribbean, complete with a flamboyant, girly-man pirate and a Greek chorus of ghostly princes.
The story concerns young Tristan, who sets out to win the love of a beautiful but shallow girl by bringing her a star that has fallen into a dangerous and magical land. Tristan becomes the protector of the star--which has taken the form of an irascible beauty--who is pursued by the fraternity of ambitious, fratricidal princes and a sorority of badly aging, cackling witches.
Along the way Tristan and the star, Yvaine, meet up with an extraneous pirate ship with a don't-ask-don't-tell culture. Robert De Niro is Captain Shakespeare, the tough-talking pirate chief whose loyal crew "aargh"s on cue and keeps his cross-dressing penchant under wraps (pun intended). They sail the skies, buoyed by a dirigible; they don't really advance the plot, but they add goofy fun and a connection between earth and sky, magical and muggle.
The witches hunt Yvaine in order to cut out and eat her still beating heart -- it's their black magic Oil of Olay. Michelle Pfeiffer leads the sisters in their witchy quest for the star, using the dregs of the last eviscerated star to restore her villainous beauty.
Stardust is too long and too convoluted to be a true classic, but it has plenty of charm and whimsy to keep you caring about Tristan and Yvaine to the fairy-tale ending.