Courtesy of Jessica Miglio

Stephen King's eight-novel multiverse has been turned into a slice of lean-and-mean metaphysical action pulp, featuring a stylishly stoic Idris Elba and a magnetically evil Matthew McConaughey.

As a critic, I know I’m supposed to do my homework. So let me confess right up front that I did not prepare myself to review “The Dark Tower,” the droolingly anticipated film version of Stephen King’s multiverse novel series, by consuming all eight books in the series. I had a go at “The Gunslinger” back in the ’80s (my one period of submersion in all things King), but I never followed through on the sequels. And when I learned that the movie version was going to clock in at a mere 95 minutes, I thought: It’s clear that the filmmakers have taken the 4,000-plus pages of King’s time-tripping, parallel-universe-hopping genre mash and compressed them into something that doesn’t pretend to be a page-by-page transcription of the novels. As a result, I decided to devote myself to what’s up on screen instead of what isn’t there.

Here’s what I saw. “The Dark Tower” has been plagued by tales of last-minute re-editing and multiple cooks in the kitchen, but the movie that’s come out of all this is no shambles. It aims low and hits (sort of). It’s a competent and watchable paranoid metaphysical video game that doesn’t overstay its welcome, includes some luridly entertaining visual effects, and — it has to be said — summons an emotional impact of close to zero. Which in a film like this one isn’t necessarily a disadvantage.

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The movie, which centers on Jake Chambers (Tom Taylor), a teenager with psychic powers who becomes the epicenter of a battle for the fate of Earth, suggests an “X-Men” installment with exactly one underage mutant crossed with “The Shining” crossed with “The Book of Eli” crossed with “The Matrix” all wrapped up in enough pow! pow! blam! blam! to leave viewers who don’t even know who Stephen King is feeling like they’ve gotten their money’s worth. A few of the concepts drifting through the film suggest how far ahead of the curve King was, a few play as flagrantly derivative, but when you watch “The Dark Tower” you may not bother to separate the Kingian from the Jungian from the ready-made-for-DVR-ian. It all fuses into a glittering trash pile of déjà vu action pulp.

Jake, a kid from New York, is consumed by spooky visions of another world that he’s compelled to sketch into drawings. They include images of a mechanistic volcano, of human beings with fake skin, and of a glowering Man in Black and a hero known as the Gunslinger. Jake’s visions are all real, but everyone thinks he’s seeing things, including his mother (Katheryn Winnick), who arranges to send him to a psychiatric retreat. But one of its workers has the seared skin out of Jake’s nightmares. So Jake escapes, finding his way to a crumbling house in Brooklyn, where he goes through a portal that looks like a ’70s Spielberg light show.

He emerges in a rocky wilderness known as Mid-World, and it’s there that he meets the Gunslinger, Roland Deschain (Idris Elba), a stoic avenger in a frayed leather trenchcoat whose mission is to protect the Dark Tower, a force of cosmic good that’s been around since the start of time. The Gunslinger’s nemesis, the Man in Black (Matthew McConaughey), is out to destroy the Tower, and if he’s allowed to do so the universe will collapse. The Man in Black operates out of that sinister volcano, a medieval sci-fi lair where he places gifted children in a head-locking “Matrix” chair that sucks out their energy to destroy the Tower (or something), and what pulls you into the movie is McConaughey’s spiffy portrayal of evil with a dry-ice leer.

Sauntering around in spiky jet-black hair, he looks like the dark brother of Siegfried and Roy crossed with the world’s most lean-and-mean Elvis impersonator. Yet what makes the Man in Black nifty-campy-scary is the ominous nonchalance with which McConaughey imposes his power, commanding people to kill themselves on a whim (“Stop breathing!” he snaps at Jake’s icky stepfather, and the dude does, and dies). McConaughey makes the Man in Black a neatly purposeful demon, a roving executioner with style.

For a while, Idris Elba seems a little blank by comparison, but that’s just because the Gunslinger is biding his time. He’s got a deeply personal beef with the Man in Black, who killed his father (Dennis Haysbert), and he’s a broken but unbowed cowboy knight, with a pistol forged from metal right out of Excalibur. You’re all but waiting for the moment when he travels with Jake through a portal back to earth, a place that believes in bullets. In Manhattan, Elba’s recessive cool blossoms into badass swagger, and the protector/kid bonding takes. Tom Taylor is a good young actor who radiates tensile anxiety, even though he looks like he’s going to grow up into Jon Bon Jovi. Jake has been graced with the gift of seeing all, but he still has lessons to learn, like the proverbial one taught by the Gunslinger: “He who shoots with his hand has forgotten the face of his father.” This translates, roughly, as: “May the Force be with your ass-kicking.”

With any luck, “The Dark Tower” could be a solid box-office performer (at least, for a weekend), yet the picture’s no-frills design raises an interesting question: Would it be a more commercial movie if it were an ambitious, two-hours-plus sprawl that tried to stay digressively true to the layered weight of King’s novels? My instinct says that no, that movie would have been a slog. “The Dark Tower” works as a film because it’s not trying to be a multiverse — and because, in its forgettable derivative ballistic way, it packs in just enough of the King vision to remind you that everything old can be new again, especially if it wasn’t all that novel the first time.