Of all the doom-laden fantasies the studios have rolled out this summer, “Pacific Rim” is the one pushing itself most aggressively as guilt-free entertainment, offering up an apocalyptic spectacle in a spirit of unpretentious, unapologetic fun. Which it will be, at least for those who measure fun primarily in terms of noise, chaos and bombast, or who can find continual novelty in the sight of giant monsters and robots doing battle for the better part of two hours. Viewers with less of an appetite for nonstop destruction should brace themselves for the squarest, clunkiest and certainly loudest movie of director Guillermo del Toro’s career, a crushed-metal orgy that plays like an extended 3D episode of “Mighty Morphin Power Rangers” on very expensive acid.

Although this epic gamble from Warner Bros. has generated considerable anticipation among del Toro’s fanbase, it remains to be seen whether a non-franchise property, rooted in the Japanese Kaiju tradition that spawned Godzilla among other legends, can generate the sustained B.O. needed to offset a nearly $200 million production budget. International prospects look strong if nothing else, especially around the Pacific Rim itself, where the picture’s numerous Asian elements, not least co-lead Rinko Kikuchi, can be counted on to have particular appeal.

With this gargantuan passion project, del Toro means to fashion a giddy throwback to the monster movies of yore and restore a sense of pure escapism to the summer movie landscape, an eminently worthy goal for a genre master of such inexhaustible imagination and knowledge of the B-movie canon. Yet while the director’s love for his material is at once sincere and self-evident, it’s the sort of devotion that winds up holding all but the most like-minded viewers at an uninvolving remove; although assembled with consummate care and obsessive attention to visual detail, “Pacific Rim” manages only fitful engagement and little in the way of real wonderment, suspense or terror. It may not reside in the same crass, soulless neighborhood as Michael Bay’s “Transformers” movies, but its sensory-overload aesthetics are at times no more than a junkyard or two away.

Del Toro and Travis Beacham’s script lays out the futuristic premise with a burst of breathless exposition: It’s 2020, and for years humanity has been at war with the Kaiju — enormous, lizard-like beasts that arise from the ocean floor to wreak havoc on coastal cities (San Francisco, Manila and Cabo San Lucas are decimated in a matter of minutes). But the tide turns when the men and women of Earth form the Pan Pacific Defense Corps and begin building Jaegers, 25-story-high fighting robots that ward off enough Kaiju attacks to achieve an uneasy stalemate.

SEE MORE: ‘Pacific Rim’s’ Legendary Marketing Challenge

In a plot point that will remind some of Japan’s popular “Neon Genesis Evangelion” franchise, each Jaeger is controlled from within by two humans, one to operate each hemisphere of the robot’s body. Hotshot American brothers Raleigh (Charlie Hunnam) and Yancy (Diego Klattenhoff) make a trusty co-piloting team, at least until their Jaeger engages a Kaiju off the coast of Alaska, spelling a hasty exit for Yancy while granting audiences their first taste of monster-vs.-robot action. The viewer’s level of appreciation for this initial bout will likely indicate how much they enjoy the rest of the picture, with its wall-to-demolished-wall action.

Five years later, a still-scarred Raleigh gets a shot at redemption from well-named PPDC commander Stacker Pentecost (Idris Elba), who wants him to take charge of his old Jaeger, Gipsy Danger, as the humans prepare to make one last stand against the ever more powerful and dangerous Kaiju. Heading to a massively fortified version of Hong Kong, Raleigh finds an ideal Gipsy co-pilot in Pentecost’s demure but formidable young protege, Mako Mori (Kikuchi), whose appointment sets off literal and figurative sparks.

The story’s most intriguing angle is the trippy process by which two fighters power a Jaeger, requiring them to enter into a unique state of mental and bodily fusion called “the Drift.” That Raleigh and Mako must share each other’s thoughts, feelings and memories is a conceit that would seem to raise any number of tantalizing dramatic possibilities, and there is one memorable flashback to Mako’s childhood — an episode that, in evoking the atomic horrors that spawned the Godzilla legend, briefly recalls the nightmarish fairy-tale intensity of del Toro’s 2006 masterwork, “Pan’s Labyrinth.”

SEE MORE: Inside ‘Pacific Rim’ with Guillermo del Toro

In all other respects, the script is content to skim the surface. The psychological effects of the Drift are not dramatized but assumed, the progression of the story not developed so much as programmed. (“I can’t have anyone else in my head again,” Raleigh says, a curious complaint from a hero about whom we know almost nothing by film’s end.) Del Toro’s trademark humor does emerge in an overlong subplot involving Dr. Newton Geiszler (an overamped Charlie Day), a hysteric-prone scientist attempting to figure out the monsters’ master plan, and Hannibal Chau (an obligatory appearance by del Toro fixture Ron Perlman), a pimped-out black-market dealer in Kaiju body parts.

Here and there, “Pacific Rim” reveals hints of a potentially rich but underdeveloped science-fiction mythology, full of satirical and speculative touches that are ultimately overwhelmed by the fight sequences that represent the film’s raison d’etre. Overkill is not just the goal but a governing artistic principle, and del Toro takes it on such faith that nothing could be more compelling than his monsters-and-robots mash-ups that he spends almost no time easing us into the fray. The pacing is mechanical, even bludgeoning, in its single-mindedness. Buildings topple and bridges collapse; the mid-ocean battles are so ferocious that mankind would surely be wiped out by the resulting tidal waves, if not the monsters themselves. Yet such is the blithe, upbeat spirit of the whole enterprise (“Today we are canceling the apocalypse!” is the film’s signature rouse-the-troops line) that nothing in these gladiator-style faceoffs feels at stake, except perhaps the viewer’s desire to see a Jaeger swing an aircraft carrier like a 2×4.

One of the picture’s persistent problems is that its man-meets-machine conceit never really comes to life, resulting in a strange disconnect between these metal marionettes and the humans at the controls; aside from a few impressive payoffs, as when Mako’s ingenious maneuvering saves the day, the overall experience is not unlike that of watching someone play a highly elaborate videogame. The whooshing cinematography by Guillermo Navarro (lensing his first picture in digital) and the rapid-fire editing by John Gilroy and Peter Amundson conspire to create a metronomic visual rhythm with little sense of mounting excitement, an effect unaltered by the film’s post-production 3D conversion (it will also be released in stereoscopic Imax).

SEE MORE: Kanye West’s Praise for ‘Pacific Rim’ Ignites Buzz

As conceived by a small army of concept artists, sculptors and designers, and seamlessly animated by a larger army of ILM visual-effects artists, the combatants are arresting enough to behold when you can see them clearly — particularly the Kaiju, some of which are equipped with sharp appendages capable of impaling their opponents and/or squirting bioluminescent venom. Enhancing this glow-in-the-dark effect, almost all the major setpieces unfold at night against futuristic cityscapes brushed with vibrant neon hues.

Rounding out the fine if underused ensemble are Clifton Collins Jr. and Burn Gorman as gifted, eccentric members of the Kaiju-fighting initiative, and Max Martini and Rob Kazinsky as an Australian father-son pilot duo who add some dramatic tension to the mix. (In the spirit of international cooperation, Chinese and Russian Jaeger teams also make token appearances.) Hunnam reps a blandly serviceable lead, but Kikuchi manages to render her character’s shrinking-violet reserve as intriguing as her sudden displays of physical prowess. Too often the actors, including the terrific Elba, are forced to bellow over Ramin Djawadi’s omnipresent score, likely to be ringing in viewers’ heads as they stagger toward the exits.