What would happen if the 50-Foot Woman teamed up with The Blob, The Fly, The Creature from the Black Lagoon and a larval Mothra to battle a giant robot from space and an alien invasion?

That’s not precisely what you get in Monsters vs. Aliens, the latest computer-animated genre send-up from DreamWorks Animation, but it gets you in the ballpark.

A New York Times story reports that directors Rob Letterman and Conrad Vernon researched their subject matter by watching 150 B-movies from the 1950s, ’60s and ’70s. I believe it.

The opening sequence, in which would-be bride Susan Murphy (Reese Witherspoon) is exposed to mysterious energy by a meteorite that nearly falls on her on her wedding day, then proceeds to swell to the gargantuan proportions of Ginormica, isn’t copied from Attack of the 50-Foot Woman or any other ’50s film, but it feels like a piece of that world.

Same goes for Dr. Cockroach (Hugh Laurie), who isn’t exactly The Fly, and the Missing Link (Will Arnett), who isn’t exactly the Creature from the Black Lagoon. The titanic Insectosaurus, who towers over even Ginormica, is at least as much Godzilla as Mothra.

As for the gelatinous, literally brainless B.O.B. (Seth Rogen), well, he isn’t much like anything you’ve ever seen anywhere outside of a computer-animated film, but he’s the most reliably entertaining thing in the film, both script-wise and visually.

Monsters is easily DreamWorks’ most ambitious and spectacular computer-animated effort to date. The worlds of the Shrek and Madagascar films have always felt somehow paltry and half-hearted to me, as if the characters themselves didn’t believe the picture extended beyond the edges of the screen, or that the story extended beyond the opening and closing credits. Only Kung Fu Panda created a persuasive and satisfying alternate reality.

Monsters does something similar, but on a far larger scale, with secret government compounds, cavernous alien spacecraft and epic disaster-style set pieces — and in eye-popping 3-D (at some theaters) it’s a sight to behold.

Perhaps kung fu and sci-fi monsters bring out the inner geeks of the DreamWorks animation teams better than fairy tales and other things they’ve tried.

If the supporting cast isn’t very well realized or utilized, well, neither were Kung Fu Panda’s Furious Five. But where Panda focused on the relationship of enthusiastic Po and gruff Master Shifu, Monsters only has one character that really matters: Ginormica.

More seriously, where Po’s acquisition of discipline, self-confidence and skill made his journey from hapless kung-fu fan boy to Dragon Warrior a satisfying one, Ginormica’s story — a feminist fable of grrl power and male inadequacy — is more irritating than engaging.

In some ways, it’s even the same story as her counterpart in Attack of the 50-Foot Woman. In both stories, the heroine is pursued by aliens who want her for a power source in her possession.

In both films, she’s initially unassertive and blind to the shortcomings of her self-centered man, who abandons her to institutional custody and whom, in a climactic scene, she manhandles like a rag doll.

And she has wardrobe issues — not only does her growth spurt leave her barely dressed, she spends the rest of the film in skin-tight cat suits accentuating her Barbie-colossus curves.

Monsters opens on a promising note, with the hopeful bride preparing for a church wedding and a teary prenuptial father-daughter scene, before fiancé Derrick (Paul Rudd) shows up. The first sign of trouble isn’t that Derrick, a small-town weatherman with dreams of big-network glory, wants to cancel their Paris honeymoon to go to Fresno for a job interview. It’s that he pitches this to Susan as great news, rather than telling her how sorry he is.

Disappointed, Susan is gamely supportive — “As long as I’m with you, Fresno is the most romantic city in the world.” — an attitude that could bode well for their future in a story in which someone like Derrick was capable of enlightenment. In this world, though, it means that Susan is a passive victim of Derrick’s egotism.

“Derrick is a selfish jerk!” Ginormica exclaims angrily after a reunion as painful as it is brief. “Why did I have to get hit by a meteor before I saw it?”

Besides waking up to Derrick’s selfishness, Susan needs to overcome her timidity, stop “shortchanging” herself — yes, that feminist buzzword is actually used — and trust her own strength.

In an age of fearless heroines like Tigress, Coraline, Elastigirl, Elizabeth Swann and Hermione Granger, is this a story children will relate to? (Yes, The Incredibles’ Violet needs to learn self-confidence, but she’s (a) a painfully shy teenager (b) who’s been told for years to hide her gifts. Susan’s a grown woman with nothing more oppressive in her known past than loving parents and a suburban milieu.)

Will youngsters even understand why, in the first big battle sequence, Ginormica and her male fellow monsters all seem to assume that the thing to do is for Ginormica to run away while her human-size teammates take on a giant alien robot without her strength?

Heck, I’m not sure I understand it. She’s obviously the only one remotely in the robot’s league. (Insectosaurus isn’t on the scene yet, and it’s not clear he understands anything at all.)

Susan’s callow fiancé Derrick isn’t the only embodiment of male inadequacy. The Missing Link sulkily nurses a wounded ego when his braggadocio is squelched following the giant robot battle, in which Ginormica shines while he ineffectually stands by.

The President (Stephen Colbert), after grandly trying — and failing — to communicate with the alien robot through music, screams like a woman when shown an image of Ginormica, evidently threatened by powerful women. (The scream is actually a decent gag, following repeated stereotyped screams from a female character when images of the other monsters are shown.)

A superfluous scene depicting a young couple parking in a convertible at night first ridicules the virility of the young man, a letter-wearing jock (the girl wants some action and is clearly disappointed by her beau’s diffidence) — then depicts him trailing fearfully behind his intrepid date as she goes to investigate a mysterious crash in the distance. He even twists his ankle so that she has to carry him.

Other male characters fare little better. Dr. Cockroach is a typical movie egghead, besides looking like something you’d want to step on.

In a gag with a hint of gender-bending, the B.O.B.’s perennial state of confusion causes him to continually mix up his teammates with each other and even himself, so that he repeatedly believes that he — rather than Ginormica — is engaged to Derrick (in a climactic gag he indignantly “breaks up” with Derrick).

As a tale of female empowerment and male comeuppance, Monsters vs. Aliens might have been provocative, like, 50 years ago.

Today, nothing seems more subversive — and unlikely — than a family film with a heroic leading man who’s the equal of the leading lady, one boys can look up to without having to learn a lesson about male weakness.

Now that’s a movie I’d like to see.

Steven D. Greydanus is editor

and chief critic at DecentFilms.com.

Content advisory: Mild crude language and some vulgar humor; brief mildly suggestive content; cartoon sci-fi action violence. Might be too much for very sensitive youngsters.