You have to give Matthew Vaughn credit for doing something different. The director, whose debut feature was the fast-moving contemporary crime drama “Layer Cake,” follows it up with an opulent, quirkily comedic fantasy that represents a radical departure from what worked for him—at least with most critics—the first time around. It’s rather like what Ridley Scott attempted in 1985 when, after “Alien” and “Blade Runner,” he gave the world “Legend”—the movie that Tom Cruise has always tried to erase from his resume—and stumbled badly in the process.

Like Scott’s picture, “Stardust” is a fantastical piece, but it’s livelier and jokier, going more for the tongue-in-cheek feel of “The Princess Bride.” While it has its moments, though, it’s not that picture’s equal by any means—it lacks the unerring ability to juggle tones that marked Reiner’s film, and adds to the mix an avalanche of special effects that smack more of the Terry Gilliam of “The Adventures of Baron Munchausen” and “The Brothers Grimm” than of George Lucas. So it winds up seeming heavy-handed, like an elephant trying to dance ballet—a movie about magic that’s just not magical enough.

“Stardust” began life as an elaborate comic mini-series in 1998 with text by Neil Gaiman and delicate watercolors and drawings by Charles Vess. (The four issues were, of course, later reprinted in a single volume.) This adaptation retains the busyness of plot and sumptuous look of the original, but the screen proves a less inviting environment for it all. The setting is an imaginary wall somewhere on the British Isles that separates England from the supernatural kingdom of Stormhold; just on the English side is the village of Wall where the nerdy Tristan Thorne (Charlie Cox) lives. He’s unaware that his dad once crossed the wall into Stormhold and enjoyed an evening with a servant girl there, leaving Tristan as the result. The young man’s preoccupation isn’t the circumstance of his birth, but his infatuation with the lovely though egotistical Victoria (Sienna Miller), who plans to wed snooty he-man Humphrey (Henry Cavill).

But Tristan makes Victoria an offer: he’ll cross the wall and secure for Victoria the remnant of a falling star they’ve just seen land if she’ll agree to marry him instead. It’s not easy getting past the aged but surprisingly spry watchman (David Kelly, made up to look like a leprechaun), but he does, and soon finds the star—who turns out to be a gorgeous but distinctly brusque young woman called Yvaine (Claire Danes), whom he captures and tries to take back to Wall.

That’s just the start of the adventure, however, because Yvaine—and a ruby necklace she’s found—are being sought by others. One group consists of the three surviving sons of the late king of Stormhold (Peter O’Toole), who are trying to kill each other off because the last one standing will be the new ruler (four already-dead princes watch over things like a ghostly Greek chorus, to be joined by their brothers as they’re removed from contention). The successor to the crown cannot be recognized until he has not only survived his siblings but recovered that ruby, and so the final brother Septimus (Mark Strong) is in hot pursuit. Yvaine is also being tracked by three witches who can restore their youth and beauty by devouring the fallen star’s still-beating heart. Lamia (Michelle Pfeiffer), the leader of the sisters, goes off to get the girl, using her magic along the way while her siblings back home occasionally cut open animals they keep caged in the castle to divine the future by consulting the entrails and give her instructions.

But that’s not all. There are other colorful characters that Tristan and Yvaine meet along the way—romance gradually blossoming between them in the process, of course. The most notable is surely Shakespeare (Robert De Niro), captain of a flying pirate ship, whose gruff exterior hides the fact that in private he’s not only ostentatiously, and happily, gay but absurdly helpful to the travelers. But that’s not to forget Ferdy (Ricky Gervais), a fast-talking fence; Bernard (Jake Curran), an unlucky peasant Lamia turns into first a goat and then a woman; Billy (Mark Williams), a goat she transforms into a not-quite-finished man; and Tristan’s mom (Kate Magowan), who turns out to be the key to an ending that’s not only happy but redolent of the final crowded-hall scene from the first episode of “Star Wars.”

As all this should make clear, Gaiman borrowed from multiple sources when writing “Stardust,” and in this adaptation the inspirations are all too evident—from Tolkein and “Peter Pan” to a far less joyous Disney flick, the dreadful three-witches comedy “Hocus Pocus.” Some parts of the mix come off pretty amusingly—the inserts involving the dead princes are fun in a “Canterbury Ghost” sort of way, Kelly’s and Gervais’ scenes are enjoyable, and O’Toole pulls off a delicious cameo as the dying king. And one has to give Pfeiffer and De Niro praise for trying something so unusual, even if their efforts don’t completely work. Pfeiffer’s the more successful of the two—as in “Hairspray,” she does the Cruella De Vil bit well—but the big final battle sequence between her and Tristan (in which she uses Septimus as her pawn) is so bloated that even she gets lost in the effects. (The appearance of what looks like Gumby’s cousin in the sequence is also laughable, though not in a good way.) De Niro works extremely hard to bring off the stereotype of the swishy drag queen trapped by he-man expectations, but in the end he doesn’t seem much more comfortable here than he was in “The Adventures of Rocky and Bullwinkle.” As with Dustin Hoffman in “Hook,” it’s a casting choice better in theory than in reality.

But it’s the weakness of the romantic stuff at the center of the story that ultimately dooms “Stardust.” Cox comes across like an even blander version of Orlando Bloom from the “Pirates” movies, and the Tristan-Victoria-Humphrey material falls flat (with Miller simply boring). Worst of all, though, sparks never fly between Tristan and Yvaine, who, as Danes plays her, is attractive on the outside but rather brittle and unpleasant in terms of personality. It’s somehow symptomatic of the love story that its best moment comes at the point that Tristan has been turned into a rodent and Yvaine has to pour her heart out to the cute little mouse.

“Stardust” has been produced on a lavish scale, and Ben Davis’ expert Panavision cinematography certainly accentuates the strengths of Gavin Bocquet’s production design, Peter Russell’s art direction, Peter Young’s sets and Sammy Sheldon’s costumes. But Ilan Eshkeri’s score is generic, and the effects, especially in the big battle scenes, are splashy but lack the ultimate in texture and clarity.

You have to admire the ambition of “Stardust.” But as with another recent release with celestial allusions—Danny Boyle’s “Sunshine”—in the end it’s the sort of movie you respect more for its unfulfilled aspirations than its actual accomplishment.