"The man in black fled across the desert, and the gunslinger followed." Thus began Stephen King's "The Gunslinger," the comparatively slim 1982 novel which kicked off the mammoth, 4,250-page, eight-book fantasy series "The Dark Tower." In a collective literary opus which took the author three decades to complete, his imagination knew no bounds as he crafted one of the finest, most immersive examples of world-building ever put to page. Long thought unfilmable, the source material has been transferred to screen via a massive retooling that somehow combines all the books and virtually none of them at all. Standing confidently on its own yet crying out for a deeper dive, "The Dark Tower" is alternately savvy and frustrating—savvy because it somehow cohesively and engrossingly tells its complex story while avoiding lumbering exposition, and frustrating because there is so much untapped potential that will only see the light of day if this genre-bending $60-million adventure is a financial success.

The gunslinger of that opening sentence is Roland Deschain (Idris Elba), a barely mortal Mid-World war vet looking only for vengeance. The man in black is Walter (Matthew McConaughey), a malevolent sorcerer who has killed everyone Roland loves. Caught in between their chase is Jake Chambers (Tom Taylor), a 13-year-old from Manhattan with the psychic power to "shine." Receiving visions of these two men and the alternate realm from which they come, Jake is told by his worried mother (Katheryn Winnick), his callous stepfather (Nicholas Pauling), and psychologist Dr. Hotchkiss (Jose Zuniga) that the fantastic pictures he draws are born from dreams and the feelings of an encroaching darkness threatening to take over the world are all in his mind. Jake knows better, and when he finds himself transported to Mid-World he soon becomes involved in Roland and Walter's feud. A larger battle, however, approaches. Looming at the center of the universe is a mystical structure called the Dark Tower. As long as it stands, it protects us from an apocalyptic fate filled with demons and monsters. Walter is aware that the mind of an extraordinary child is the only thing powerful enough to bring it, and he has Jake in his crosshairs.

"The Dark Tower" has been confidently directed by Nikolaj Arcel (2012's "A Royal Affair") and co-written by Akiva Goldsman (2017's "Rings") & Jeff Pinkner (2014's "The Amazing Spider-Man 2") and Arcel & Anders Thomas Jensen (2015's "The Salvation"). Adapting such a massive series into its own workable shape must have been a daunting undertaking, yet the results demonstrate a smartness and economy in the act of cinematic storytelling, covering a lot of ground and doing it primarily through the strength of its dynamic construction and visuals. Running a lean, focused 95 minutes, the film has no time for self-indulgent excess as it sets up its trio of well-defined if somewhat undernourished central figures: the stoic but not unfeeling Roland, thirsting for retribution; the evil Walter, who turned to killing Roland's loved ones when he learned the gunslinger had the power to resist his magic; and young Jake, intrinsically linked to both of them and a wider universe in peril.

Tom Taylor, making his major feature debut, is a real find as Jake Chambers; it is from his point-of-view much of the narrative unfolds, and he is an instantly sympathetic protagonist with a gift for naturalism and emotional truth. Jake's relationship with Roland, who is initially suspicious of this mysterious child but gradually comes to love him like a son, is the movie's purest, most endearing element. It helps, of course, to have a talent of Idris Elba's (2016's "Star Trek Beyond") potent stature taking on Roland; while Roland's tragic backstory is only cursorily touched upon, Elba is able to expressively fill in the gaps of a man who has tried to shut off his emotions—with little success—as he hunts down the man in black. As the savage devil-in-human-form Walter, Matthew McConaughey (2016's "The Sea of Trees") puts an affectingly grim spin on the actor's frequent good-time persona; his is a strong performance—stronger, perhaps, than the streamlined way in which the man in black has been penned.

Audience reaction from fans of Stephen King's "The Dark Tower" will likely be divisive. Most will be unable to escape their yearnings for what could have been if money was no object and a studio committed up front to spinning the tale as originally imagined. Going in with the knowledge this is not a direct translation of the novels, however, goes a long way in being able to view it as its own entity. This is, after all, how any film deserves to be judged, and perhaps this is a case where audiences unfamiliar with the books might appreciate it more because they have no reference to compare.

Whatever the case, the film works more often than not, a muscular yet appreciatively unshowy conjuring of spectacle, action, and crucial character beats all playing out on a multi-plane tableau melding reality with sinister fancy. When director Nikolaj Arcel is able to open up his surroundings while hinting at an even greater universe as yet unexplored, the proceedings zing with ingenuity and promise. In addition to the threatening "All Hail the Crimson King" graffiti found in the Brooklyn brownstone where a portal to Mid-World exists (those in the know will be aware this as-yet unseen force is to become the big heavy), references and Easter eggs to King's voluminous oeuvre thrillingly abound. A set-piece at a long-abandoned theme park doesn't quite land—the lighting appears too dark, perhaps to shield the seams of a CG-designed creature—but the haunting simplicity of the place itself is beautifully portrayed, and one would be remiss to overlook the harbinger of a "Pennywise" sign looming across from a bouquet of forgotten balloons.

"The Dark Tower" is a satisfying work of shifting genres and inspirations, a desert-strewn western sharing time with that of a modern horror-thriller, an epic fantasy, and an intimate human story of fathers and sons (both Roland and Jake have lost theirs, but are guided by the valiant principles on which they were raised). A third-act one-on-one battle between the gunslinger and the man in black is possibly its weakest link; in a saga bursting with so much ambition, why does this fateful climax take place in a dank, aesthetically nondescript room? Fortunately, the heart of the picture lies with Roland and Jake, and it is the care with which this bond develops that is most compelling. To be sure, a larger story lingering just beneath the surface of this one is fighting to get out. Whether audiences ever get to see it will decide whether "The Dark Tower" is either a decent standalone feature, or simply the deliciously suggestive start to something altogether better, grander, and deeper.