Small-time publisher Timothy Cavendish (Jim Broadbent) describes the creative process: Sometimes you slay the dragon. Sometimes the dragon slays you.

That sums up the approach to “Cloud Atlas,” in which a dizzying series of epic challenges are faced by the movie’s characters … and its filmmakers. Andy and Lana Wachowski of “The Matrix” series and Tom Tykwer of “Run Lola Run” join forces to tackle this year’s biggest cinematic dragon. (It’s one of the few films in history to share equal credit among three directors.) They don’t win every skirmish with the beast, but they ultimately emerge victorious.

Their formidable drama spans hundreds of years, with cast members including Broadbent, Tom Hanks, Halle Berry and Hugo Weaving portraying numerous characters in all manner of disguises. The six primary story lines are linked in ways both subtle and obvious, with each based around the idea of revolution (thankfully, not “The Matrix Revolutions”).

The film is adapted from David Mitchell’s 2004 novel, whose title refers to “The Cloud Atlas Sextet.” This musical opus rooted in overlapping soloists is the work of Robert Frobisher (Ben Whishaw), a gay composer in 1936 whose modernist slant riles his famed mentor and employer (also Broadbent). The malleable melody of his piece — which features notations shaped like ascending clouds — turns up as a connective leitmotif throughout the picture.

The other sections of the story involve the slave trade of 1849, an investigation into a nuclear power plant scandal in 1973, a comedic escape from a nursing home in present day England, a totalitarian government being defied in 2144 and a post-apocalyptic 24th century.

Perhaps the most surprising aspect of this nearly three-hour saga is how quickly it moves. Each of the six portions is packed with action. The split narrative allows filmmakers to jump to another storyline if one starts to languish. It’s like a “Monty Python” episode: Don’t know how to finish a sketch? Cut to something completely different.

While each of the installments is interesting — and, at times, awkward — the standout is the 2144 sequence. It’s an astonishingly vivid dystopia, seen through the eyes of a fast-food worker clone named Sonmi-451 (a powerful Doona Bae). The setting is Neo Seoul, a glossy Asian metropolis that combines the most oppressive aspects of “Gattaca,” “Minority Report” and that 1984 Apple Macintosh ad.

The press of a button can digitally transform a gray, concrete room into an oasis of blue skies above and orange koi swimming under glass below. But deep down the gray remains.

Sonmi is rescued from her slave-like existence to be a revolutionary oracle. Truth is singular. Its versions are mistruths, she broadcasts.

It’s equal parts eerie and thrilling.

Least successful is the one in Hawaii “106 winters after the Fall,” with Hanks as a tattooed goatherd and Berry as a tech-savvy missionary. It’s all a bit hokey, especially whenever phantom-like Old Georgie (Weaving) makes an appearance for Hanks’ eyes only. Decked in a top hat, he’s a ridiculous mix of the ’90s “Leprechaun” horror flicks and the Child Catcher from “Chitty Chitty Bang Bang.” It doesn’t help that this entire section is delivered in “A Clockwork Orange”-style pidgin that renders every other sentence unintelligible.

Here and elsewhere there is something a tad off about the casting. Oscar winners Hanks and Berry appear less comfortable with the multiple roles than the more chameleon-like character actors who take second billing. Wigs, prosthetic noses and fake teeth can prove distracting for a performer, creating distance rather than connection. Perhaps that’s why the two most resonant lead performances arise when Broadbent and Bae look the most like themselves.

Regardless, “Cloud Atlas” is the year’s most ambitious film. It embraces its radical structure, time jumps and plural roles. And for a project so out there, its optimistic message seems clear.

As Bae’s subversive Sonmi explains, “From womb to tomb, we are bound to others — past and present.”

What others are saying

•  Colin Covert, Minneapolis Star Tribune: “Three directors, plus six story lines, times five centuries equal one grandly conceived, impressively mounted megaflop. ‘Cloud Atlas’ gene-splices genres, spans planets and leap-frogs millennia until it time-trips on its nose.”

•  Rex Reed, New York Observer: “Almost three hours long, a lugubrious sludge of mud soup called ‘Cloud Atlas’ deserves a limp nod for pure guts, I suppose, but what I’d really like to do is burn it.”

•  Tim Robey, The (London) Telegraph: “Far and away the most divisive film of 2012, but I don’t think it’s possible to fault it for shortage of chutzpah. … There’s plenty to argue with, more to scoff at, and some uninitiated viewers may well choose to check out of engagement early. But it’s also a dizzily generous ride, scored with real grandeur, and even its silliest elements are guilty pleasures.”

•  Mick LaSalle, San Francisco Chronicle: “The filmmakers are betting on audiences being both willing to pay close attention, as underlying connections emerge, and willing to go along for a ride, without a clue as to the destination. The filmmakers are gambling, in fact, on the intelligence and patience of the sci-fi action audience. Let’s wish them luck.”