It’s robots vs. monsters, plain and simple, in Guillermo del Toro’s "Pacific Rim," an $180 million indulgence of the fanboy director’s affinity for Japanese pop culture.

A fissure at the bottom of the Pacific Ocean has opened a portal through which fearsome "kaiju" ("monsters") launch attacks at seemingly random intervals on Manila, Tokyo and other coastal cities — but curiously not Hawaii (guess we’ll have to wait for Godzilla, the godfather of kaiju).

‘PACIFIC RIM’ Rated: PG-13 Opens today

After the first attack on San Francisco — goodbye Golden Gate Bridge — nations put aside their geopolitical differences to build a fighting force of high-rise robots called Jaegers (that’s German for "hunter," we are told). The mecha warriors are at first able to beat down each successive kaiju that emerges from the deep.

Credit Del Toro, who co-wrote the screenplay with Travis Beacham, for jumping right into the action. Most creature features tease audiences with long stretches of exposition and unsatisfying glimpses of the monster to build suspense and save on the cost of digital effects, but the colossal kaiju and mighty Jaegers are observed in full Rock ‘Em Sock ‘Em mode within the first minute of "Pacific Rim."

As explained in the lengthy prologue narrated by Raleigh Becket (a buff Charlie Hunnam, Jax on FX’s "Sons of Anarchy"), the robots are so big it takes two rangers wearing special armor to operate them, each one maneuvering separate hemispheres of the Jaeger’s frame via a neural linking called "drifting." Raleigh, of course, is an impetuous hotshot, and his older brother and co-pilot is killed when they disobey orders on a mission in the waters off Alaska.

A dispirited Raleigh quits the program and hires on with the construction crew erecting a kaiju defense wall along the western U.S. coastline (good luck with that!). When more destructive versions of the monsters begin to surface and their attacks become more frequent, Raleigh’s former commander Stacker Pentecost (Idris Elba) arrives on the job site to talk him into rejoining the Jaeger squad.

The rebellious Raleigh suits up with martial arts cutie Mako Mori (Reiko Kikuchi of "Babel") to pilot his old, upgraded Gipsy Danger robot. The action-figure-ready Jaeger-meisters include the Crimson Typhoon from China, outfitted with four arms and buzz-saw appendages;

Russia’s Cherno Alpha, piloted by a badass duo right out of "Rocky 3," and the Striker Eureka with a father-son team of cocksure Australians aboard.

The son (Robert Kazinsky, who is Ben/Warlow in the current season of HBO’s "True Blood") plays the Val Kilmer role from "Top Gun," dismissing Raleigh as a reckless maverick who gets other pilots killed. Following formula, the rivals come to respect each other as they fight side by side to save the world.

Comic relief is provided by two quirky scientists — Charlie Day ("Horrible Bosses") and Burn Gorman ("The Dark Knight Rises") — and Ron Perlman, a Del Toro regular from the "Hellboy" movies and "Cronos," as a dealer in kaiju parts on the black market.

Del Toro’s fertile imagination and art-house aesthetic are on full view here with his sea monster creations and set pieces, but don’t look for the multilayered, thoughtful storytelling of "The Devil’s Backbone" or the Oscar-nominated "Pan’s Labyrinth." The plot of "Pacific Rim" is as thin as shoji doors, the characters are one-dimensional and the dialogue is rife with cliches.

The only real terror comes during a flashback showing Mako as a little girl being pursued by a raging kaiju through the empty streets of Tokyo: That’s the movie "Pacific Rim" could have been.

Instead there are some undeniably cool visuals of the expansive Jaeger hangar, rangers maneuvering the robots in unison from inside the cockpit, and helicopters airlifting the towering iron giants and dropping them into the ocean to wage combat. In one prolonged fight scene, a Jaeger grabs a freighter and uses it to club a kaiju. But much of the action is indecipherable and the aural assault on the audience is relentless.

Although the battle scenes take place at night or in rainy weather — a familiar ploy by filmmakers to hide the rough edges of computer-generated sequences — the 3-D effects don’t muddy the picture as is often the case and, in fact, they enhance the sense of the robots’ scale.

It’s helpful to know going in to "Pacific Rim" that Del Toro, an admirer of anime and manga, has said his target audience is young fanboys and -girls. So lower your expectations for the kind of dark grittiness, intriguing characters and mind-bending plots that distinguish "Blade Runner, "Alien," "Inception" and other adult sci-fi classics, and settle in with a big bag of popcorn to enjoy a really, really awesome episode of "Power Rangers." Earplugs optional.