James Cameron embarks on another Deepsea Challenge, this one in front of the camera

James Cameron might be the closest thing the early 21st century has to its own Howard Hughes: He hasn’t begun obsessively storing his urine in mason jars quite yet, but he is determined to make three more Avatar movies, which some might argue is just as insane. But where the billionaire owner of Trans World Airlines was consumed with the dream of flying higher, the Titanic filmmaker—whose net worth is north of $900 million and whose sway as a cultural force of nature is unquantifiable—has his sights set in the other direction.

Deepsea Challenge 3D is hardly the first time that Cameron has endeavored to combine his career as a filmmaker with his passion for exploring the ocean depths, but this documentary—directed by John Bruno, Ray Quint, and Andrew Wight—is the first to make Cameron its subject, and not just its wallet. The director’s artistic endeavors have been increasingly driven by a desire to expand the limits of what film can do and see, and Deepsea Challenge 3D—in which he functions as the host, narrator, star, ego, hero, and executive producer—is in many ways the perfect summation of his ultimate purpose as both a person and a filmmaker.

At its worst, Deepsea Challenge 3D plays like good television with unprecedented muscle, the kind of visionary edutainment that IMAX and Neil DeGrasse Tyson have built their brands upon. With James Cameron, however, science always takes a backseat to wonder, as though knowledge were awe’s ugly fraternal twin. The documentary chronicles the director’s journey to the deepest known point in the Earth’s seabed hydrosphere, a stretch of the Mariana Trench called Challenger Deep. In 2012, Cameron became the first (and still only) human to ever go down there alone, successfully piloting a custom-built and privately funded craft called Deepsea Challenger to the ocean floor, where he was so overcome by the magnitude of his exploration that he almost forgot to collect the sediment samples that were so important for the trip to become about learning, and not just seeing.

At its best, the film is a staggering underwater spectacle, a cinema of attractions that outclasses each of Cameron’s previous technical achievements: Creating Pandora from scratch was impressive, but showing us previously unfathomable and unseen new frontiers of our own world is a far more profound success. While the unmanned Nereus sent live video back from these same depths in May of 2009, the images were flat and unremarkable, and viewers could feel the absence of a human filter. By going down there himself and using his unique 3-D cameras (capable of resisting an absurd degree of pressure) to genuinely direct footage from 35,787 feet below the surface, Cameron restores a palpable sense of discovery to the Earth’s final frontier. There may not be much to look at when you go too deep for most life to survive, but it’s nevertheless an astonishing thing to see.

The dive itself, however, only serves as the climax to this 90-minute feature. The brunt of Deepsea Challenge 3D is an elegant yet frustratingly staid portrait of the whole process, a traditional making-of doc that too rarely enhances understanding of what Cameron and his team achieved. The film reflects the interests of its star, favoring suspense over science whenever possible. Cameron and his team are shown secretly building Deepsea Challenger in a nondescript Sydney warehouse, where they experience all of the usual triumphs and setbacks (the most unfortunate example of the latter being the freak helicopter accident that claimed the lives of Wight and underwater cinematographer Mike DeGruy, the two men to whom this film is dedicated). It’s clear that Cameron is running the show in much the same way as he would one of his sets, but the film is uninterested—and perhaps too intimidated—to more thoroughly explore the dynamic between the director and his team of hard-nosed engineers, who enjoy his money and respect his zeal, but must have some reservations about the famous director who bought the only front-row seat to the show of their lives.

Such oversights are made all the more irksome because of how Deepsea Challenge 3D consistently threatens to become a fascinating Herzogian character study of Hollywood history’s biggest earner. The focus returns to Cameron early and often, the film beginning with a series of tastefully cheesy and mercifully brief dramatizations that introduces the director as a towheaded child, already obsessed with the mysteries of the deep. From there, it goes on to rather pointedly suggest that Cameron’s unprecedented career as a blockbuster filmmaker has only been a means of earning him the bank and the celebrity required to buy him a ticket aboard some ships that sink on purpose.

The knowledge that Cameron survived his trip to the trench gives viewers permission to feel schadenfreude during scenes of the uber-powerful director fearing for his life. (One can laugh, for example, at the face he makes when a terrifying CRACK! sounds through the hull of his sub.) Cameron is like Don Quixote with a death wish to drown, and it’s a shame that Deepsea Challenge 3D is allowed to use science as an excuse not to go the full Fitzcarraldo on its star. But if James Cameron movies have seldom been admired for their scripts, his latest is utterly impossible not to appreciate for its depth.

Correction: This review initially misidentified James Cameron as the first and only person to travel down to the Mariana Trench. In reality, he’s the first person to make the voyage solo, and to pilot around the area instead of immediately returning to the surface.