Stephen King’s humongous series of eight fantasy adventure books, totaling more than 4,000 pages, about an alternate reality where a young boy aids a gunslinger to overcome a wicked sorcerer went through years of development hell on its way to the screen, and it wouldn’t be far off the mark to say that it’s now the moviegoers’ turn to visit the infernal regions. While “The Dark Tower” isn’t as horrible as its troubled history—which also included reshoots after test screenings—might portend, it’s certainly not good, either. You might compare it to the bloated behemoths that marked the collapse of the big-budget action movie cycle that brought stardom to the likes of Arnold Schwarzenegger, Sylvester Stallone and Bruce Willis. Just think of “The Last Action Hero” with silly supernatural overtones.

The picture’s real protagonist is young Jake Chambers (Tom Taylor), a troubled NYC adolescent still grieving the death of his dad, a fireman, in a blazing building. While the city endures a sequence of earthquakes, he suffers a series of frightening dreams about a barren wasteland, the eponymous tower, a grim gunman, a malevolent-looking man in black, and a pyramid-like building where boys and girls are strapped into chairs and shocked by machines—run by creatures with “fake skin”—that drain their psychic energy, which is propelled in a brilliant wave of light in repeated efforts to bring down the tower. (The resultant shockwaves are the cause of the New York quakes.) Jake, a talented artist (as all such precocious adolescents are in such stories) systematically transfers the images from his dreams to paper and posts them on his bedroom wall.

As it turns out, Jake is a special kid—a kindred spirit with another King creation, Danny Torrance—in that he’s possessed of telepathic powers, and at an extraordinary level (or, as a so-called seer will call it, “the shine”). What his dreams are revealing is an alternate universe that he escapes into when the evil dark man’s minions attempt to carry him off. There he meets Roland Deschain (Idris Elba), the last of the noble gunslingers, a corps of western-style knights whose purpose is to protect the tower, which maintains the balance between the various multiverses that exist and, if destroyed, would lead to the collapse of all reality. The tower is being assaulted by the evil sorcerer Walter Padick (Matthew McConaughey), who not only has hordes of minions and monsters at his disposal—including a coven on Jake’s earth headed by Sayre (Jackie Earle Haley)—but can magically compel anybody, save Roland, to do anything he wants, even killing themselves. (Why is never really explained.)

The plot trajectory from this point is pretty predictable. Roland and Jake gradually bond in their battle against Padick, who in turn becomes aware of Jake’s powers and seeks to capture him in order to use them to feed the weapon that will finally destroy the tower. The battle eventually takes them all to New York before returning to Padick’s lair for a final face-off between him and Roland.

One suspects that King’s books are considerably more convoluted than the movie—at one point, for instance, Padick offhandedly refers to the fact that the bullets in Roland’s guns are made of metal from something that is the equivalent of Excalibur on earth, but that tantalizing tidbit is never followed up. Nonetheless it cannot really be said that the movie, the first big Hollywood effort of Danish director Nikolaj Arcel (“A Royal Affair”) is incomprehensible—the plot is pretty barebones stuff, silly but not terribly hard to follow (as compared to something like “Assassin’s Creed,” for instance), even if details (like the locations of portals from world to world) go unexplained.

The picture is made somewhat palatable by the cast. Taylor is a likable kid—far more so that Austin O’Brien was in “Action Hero”—and while it’s really an abuse of Elba’s talent to have him play this sort of laconic Clint Eastwood-style figure, he brings considerable authority, and a trace of redeeming humor, to the role, especially in the “fish out of water” New York scenes. Given the chance to play a snarky villain, McConaughey seems to be underplaying while he is really overplaying, turning on the oily smoothness at a range of 11 on a 1-10 scale. Whether you find that fun or irritating is a matter of personal taste. Nobody else much matters, though Katherine Winnick has a few moments as Jake’s uncomprehending mom and Claudia Kim likewise as a powerful seer, while Haley is suitably sinister as Walter’s earthly follower. Michael Barbieri, from “Little Men,” shows up as Jake’s buddy, but he’s wasted in what appears to be a part truncated in the editing room, where Alan Edward Bell and Dan Zimmerman sliced the footage down to a mercifully trim 95 minutes.

As far as the visuals go, “The Dark Tower” is not in the top rank of special-effects extravaganzas, especially when compared to another opus featuring a tower, Peter Jackson’s “Lord of the Rings” cycle. Some South African exteriors of Roland’s world are impressive, but most of the forest sequences are gloomily bland, and Ramus Videbaek’s cinematography in the New York segments lacks style. As for the visual effects, they’re just passable, with the tower and Padick’s weaponized lair looking pretty threadbare and the portal sequences unimpressive.

There have been worse adaptations of books by King, but this long-awaited one is almost guaranteed to disappoint his many fans while failing to bowl over anybody else.