Stephen Sommers, the mastermind behind the first “Mummy” movie in 1999 and its equally dumb but successful 2001 sequel, has gone AWOL on this third installment, handing over the reins to writers Alfred Gough and Miles Millar and director Rob Cohen. But despite the change in creative talent—and one in locale, too—“The Mummy: Tomb of the Dragon Emperor” isn’t much different from its predecessors. It’s a loud, silly bit of non-stop action that again comes off like a poor cousin of the “Indiana Jones” flicks—a copy of a bargain-basement ’forties serial, a genre even whose best representatives were pretty chintzy.

One might have expected better of Gough and Millar, the co-creators of “Smallville” who have shown a good deal of inventiveness and imagination in their reshaping of the Clark Kent mythology. But though they’ve moved the plot from Egypt to China (something that, in the context of the title, doesn’t make an awful lot of sense), otherwise they haven’t brought much to the party. To be sure, they’ve added a father-son rivalry subplot (which frankly makes it awfully reminiscent of the “Crystal Skull” template). But for the most part they’ve just string together a chain of hackneyed action episodes, each featuring some juvenile humor. And in the process they’ve committed a cardinal sin in such stuff—changing the rules at every step, or simply announcing new ones, so that the silliness doesn’t even possess a loony internal logic. Given the pedigree, this script is very weak.

Less is anticipated of director Rob Cohen, whose last foray into this kind of mindlessly hyperkinetic stuff was “Stealth.” He doesn’t disappoint one’s low expectations, shoveling out a succession of action set-pieces in which he hands over much of the responsibility to his CGI crew while spending most of his energy simply keeping his human actors properly in frame. And the effects are frankly not much to write home about. They’re certainly plentiful, but hardly impressive. A bunch of yeti come across as nearly comical, as do hordes of terra-cotta soldiers and an army of skeletons (a nod to Harryhausen, presumably). But the nadir is probably the simplest—an old airplane that actually looks like a model glued together from a hobby shop kit.

As to plot, it’s pretty lunatic. In a long prologue we’re told of power-hungry Chinese emperor Han (Jet Li), who built the Great Wall on the bones of his defeated enemies but fell afoul of fate when he tried to become immortal. He had his General Ming (Russell Wong) seek out beautiful witch Zi Juan (Michelle Yeoh) to learn the secret of eternal life, but in his lust for her reacted with customary cruelty when she and Ming fell in love: he killed the general and attempted the same with her, but she imprisoned him, turned into stone, in a tomb with thousands of his soldiers, where he awaits release so that he can resume his campaigns of ruthless conquest.

Enter Alex O’Connell (Luke Ford), the handsome, ambitious son of Rick and Evelyn (Brendan Fraser and Maria Bello, replacing Rachel Weisz), who’s dug up Han’s tomb. (The year is 1946.) His parents, who’ve been unaware that Alex has even left college, arrive in China, where Evelyn’s brother Jonathan (John Hannah) runs a nightclub, on an intelligence mission and take their son to task. But before they’ve even gotten reacquainted, nasty General Yang (Anthony Wong Chau-Sang) breaks up the reunion by trying to kill off the family and resuscitating Han. From there on it’s a race to Shangri La in the Himalayas, where Han must bathe in the magic waters to be restored to full immortal form, and thence to the Great Wall, which Han’s invincible terra-cotta soldiers must cross in order to become human again. Rick, Evelyn and Alex join forces to stop his dastardly plan, which—no surprise here—they do, with the help of their allies: the reluctant Jonathan; Zi Juan, who herself is immortal; her lovely daughter Lin (Isabella Leong), who’s been entrusted with the only dagger that can kill Han and serves as a love interest for Alex; a wild-eyed pilot named Mad Dog (Liam Cunningham); and those aforementioned yeti and skeletons, one of whom is actually the long-dead General Ming.

There’s a half-hearted attempt to insert some humanity into all this ruckus—Rick has to bond with Alex, with whom he’s had a rather frosty relationship, and at one point he apparently sacrifices his own life for his son. But all the characters remain cartoon figures fighting and joking their way through ridiculous circumstances, and like “The Mummy Returns” before it, “Dragon Emperor” feels like a video game projected onto a big screen. The cast largely disappears in the morass. Fraser is all manic energy and wide-eyed amazement, Bello tries to maintain her aristocratic dignity with little success, Hannah mugs ferociously and Ford is stalwart but wooden. Yeoh and Leong fare somewhat better—perhaps because they seem rather bemused by the absurdity going on around them. Jet Li, on the other hand, just glowers and sneers through a thoroughly thankless role.

It’s possible to get some amusement from the very cheesiness of “Dragon King”—the sets are garishly tacky, the exteriors almost comically phony, the model work and computer animation shamelessly low-grade. And though Simon Duggan’s cinematography puts them all in the best possible light, it can’t hide the lapses, and Randy Edelman’s score accentuates the shabbiness by relying too heavily on genre tropes. They’re all part of a package that oozes mediocrity from every frame. In an era when people have come to expect more from action movies like “The Dark Knight,” “The Mummy” tries to survive on less. It should never have been disinterred.