2.5 out of 4 stars Title The Dark Tower Written by Nikolaj Arcel, Akiva Goldsman, Jeff Pinkner and Anders Thomas Jensen Directed by Nikolaj Arcel Starring Idris Elba and Matthew McConaughey Country USA Language English

"The man in black fled across the desert, and the gunslinger followed."

The opening sentence of Stephen King's 1982 novel, The Gunslinger, remains one of the best things he's ever written. King, a writer who's never been accused of minimalism, establishes an entire world in a dozen words: "The man in black" is obviously the villain; "the desert" conjures up a lonely, dangerous landscape; and "the gunslinger followed" not only introduces our hero but injects a sense of urgency, of relentless pursuit, right off the bat. It's a marvel of concision and plot.

This being King, of course, what began as the seemingly straightforward story of a possibly immortal cowboy named Roland Deschain hunting a being of pure evil ballooned into an eight-part series that, when it concluded in 2012, had surpassed 4,000 pages and one million words. There was a spinoff novella and an ongoing comic book series.

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And that's not all. Characters from the Dark Tower universe often pop up in other King novels and stories, with events or places from the series referenced in passing. It sometimes feels like a giant Easter egg hunt. To fully understand the Dark Tower, you have to read almost all of King's work, which at last count was more than 50 novels and 200 short stories. Last year he even published a picture book, Charlie the Choo-Choo, based on the third instalment in the series, The Waste Lands, under the pen name Beryl Evans.

The Dark Tower is a very, very tall structure.

"I have written enough novels and short stories to fill a solar system of the imagination, but Roland's story is my Jupiter – a planet that dwarfs all the others," King once wrote. "Dwarfs the others, did I say? I think there's more to it than that, actually. I am coming to understand that Roland's world [or worlds] actually contains all the others of my making …"

And yet the Dark Tower has never been adapted for the screen, which is bewildering considering everything else King has ever written seems to have wound up in movie theatres or on TV. (King is a prolific Twitter user, and it wouldn't surprise me if some ambitious producer has already optioned a few of his choice tweets.)

That's not to say there haven't been attempts to scale the tower. Over the years, directors ranging from J.J. Abrams to Ron Howard were attached to the project, which was constantly being reimagined. It'll be a movie! No, a miniseries! How about a prestige TV show? (HBO was involved at one point – we can only dream.)

Yet the series King considers his magnum opus, which overshadows and interconnects almost every word he's ever published, remained on the shelf.

Until now.

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The Dark Tower that arrives in theatres is not the mammoth time-travelling, parallel worlds-encompassing genre mash-up that many readers no doubt hoped for. It contains some of those things, but it's a rather lean (a few ticks over 90 minutes) and often quiet affair, with a surprising dose of humour and heart.

It also feels like a movie whose sole purpose is to prove it could be done, like George Mallory explaining he climbed Mount Everest simply because it was there. It's not that The Dark Tower is a bad film, but it's an instantly forgettable one. And instead of kick-starting a new franchise, as its producers no doubt envisioned, it will likely ensure that no one attempts to adapt the books for many years to come.

So how do you tackle a series that, length-wise, makes The Lord of the Rings look like The Cat in the Hat? If you are Danish filmmaker Nikolaj Arcel (best known for helming the Oscar-nominated A Royal Affair), you strip away almost everything and start from scratch.

The film focuses on an 11-year-old boy named Jake Chambers (played by relative newcomer Tom Taylor) who, at the outset, is plagued by nightmares. He dreams of a man in black and creatures who wear the faces of humans and, of course, a dark tower. Jake doesn't understand his visions, but he is convinced something bad is about to happen.

Because this is a movie, the walls of his bedroom are covered with black-and-white sketches of what he has seen in his sleep. His mother and stepfather want him committed – not that you can really blame them. But before they can send him away for psychiatric treatment, Jake winds up – thanks to a magical portal hidden in a crumbling Brooklyn mansion – in Mid-World, where he almost immediately (and conveniently) runs into the Gunslinger, Roland, played with extreme detachment by Idris Elba, who is searching for the Man in Black in order to avenge his father's death.

Jake quickly learns that his dreams were in fact true: The Man in Black (real name Walter, played by Matthew McConaughey like an icky pick-up artist) is kidnapping children, whose souls (or perhaps their minds – it's unclear) are required to bring down the Dark Tower, which protects the universe. If the tower falls, demons and other monsters will flood not only Mid-World but Jake's world as well.

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When Walter learns that Jake possesses "shine" – awesome psychic abilities – he orders his minions to capture the boy in order to take down the tower once and for all. (Not that Jake is really ever at risk: Walter, despite being an all-powerful sorcerer who can kill a person with the sound of his voice, is the least malevolent villain in recent memory.)

Like the novels on which the film is based – and this is not a faithful adaptation by any stretch of the imagination – The Dark Tower mixes elements of fantasy, horror, westerns, post-apocalyptic fiction and science fiction. It is several things at once: a revenge tale, a coming-of-age story and a quest. When Roland and Jake return to the boy's native New York City, it even becomes a droll fish-out-of-water story for a rather amusing 10 minutes. It's an action film, too, though the action is limited to a couple of short shootouts and a climactic battle that borrows heavily from better films such as The Matrix and, at least aesthetically, Blade 2. And then, suddenly, it's over.

Less than 24 hours after I watched the film, I struggled to recall much of what I'd seen – it was there and then it was gone. That's not to say there aren't moments of beauty – even power. At one point, as Jake and Roland navigate the ruins of Mid-World, a once-glorious civilization brought to its knees, they come across a relic from its past. Roland treats it as a thing of great mystery, unsure of who built it or what it represents. It's a theme park, Jake replies, a rusting roller coaster emerging from the foliage like the bones of some ancient creature. The Dark Tower is King's ultimate roller coaster – twisting and stomach-clenching and terrifying but, above all, fun. If only this version was as thrilling a ride.