“Clang, bang, bang, ka-boom. On my mark! Roger that! Bang, bang, crash, boom, GRRR!, bam, bam, pew, pew, bang, crash.”

Now you’ve seen “Pacific Rim Uprising” without frittering away two hours of your life. Happy to help. I left out “Aww!” and “Yay!” in the interest of brevity, but you get the drift.

What we have here is a textbook example of an unnecessary sequel. “Pacific Rim,” 2013’s bombastic sci-fi blitzkrieg of human-piloted giant robots in smackdown fights with big alien monsters, was trash cinema. But it was rubbish raised to the level of romping good fun by the taste and virtuoso polish of director Guillermo del Toro.

Unfortunately, the franchise has been passed to fumbling hands. The follow-up, from first-time feature filmmaker Steven S. DeKnight, lacks the original’s impressive cast in well-drawn roles (Idris Elba and Ron Perlman are much missed here) and its ambition to be something more than a computer-generated demolition derby. The tone is light and pointedly kid-friendly, but the clever, playful spirit of the original is largely missing. There is more solid entertainment in a Marvel trailer. This is bad. Optimus Prime bad.

John Boyega (Finn from “Star Wars”) leads a young cast with an enthusiastic, gung-ho spirit but extremely one-note acting chops. He plays Jake Pentecost, a military dropout turned lovable bad boy. He has spent the decade since the first film’s “kaiju” monsters were chased away by “jaeger” mechanical goliaths by stealing valuable scraps from the wreckage and partying hard.

He’s attempting to pull out from the shadow of his formidable, deceased dad, Stacker (Elba), main leader of the planet’s robot guardians and epic motivational speaker. Stacker’s iconic “We are canceling the apocalypse” speech from the first film is echoed here, giving the new film one of its few grace notes.

On one of Jake’s criminal scavenging missions he meets Amara (Cailee Spaeny), an early-teens junkyard engineer who has built a little rust bucket jaeger of her own for self-defense. She intends to be ready when the next galactic threat arrives.

They form a sort of mentor/protégé partnership, his rebellious spirit guiding her inexperienced spunk. But Boyega, while he does a wicked Elba impression here, never connects with Spaeny, who may grow into being a subtle, interesting actress but isn’t there yet. Luckily, their personal stories are largely abandoned when the smashing begins.

The ensemble is cast with international diversity that feels as if people were recruited to fill roles not because they fit well, but because a dozen boxes had to be checked on the cast list. It’s understandable that Japan’s Rinko Kikuchi would return from the original film for an extended cameo. Chinese actress Tian Jing’s verbose role as a titan of industry is delivered almost entirely in subtitled Mandarin, which is probably good overseas marketing but turns into a clumsy running joke when co-star Charlie Day tries to talk to her.

The others in the globe-spanning group are as indistinguishable as the robots bashing into buildings and each other. Without any character development that makes them stand out and earn our attention, the players representing various international demographics don’t feel like colorblind casting but opportunism.

Following the example of old Godzilla movies, the large-scale fisticuffs utterly demolish Tokyo and wipe out other Asian megacities, where the detailed collapse of skyscrapers is presented as casually as if the World Trade Towers were still with us. Five years ago, del Toro avoided the unpleasant aftertaste by mostly avoiding city centers in broad daylight, staging battles at night, in rainstorms and underwater.

This movie is aimed at explosion-starved children, but how many adult guardians will see repeated doomsday images of collapsing urban centers without thinking “Too soon?” It’s hard to take the film’s gleeful nonstop destruction seriously, but it’s harder still to watch at all.

Colin.Covert@startribune.com

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Twitter: @colincovert