The filmmakers behind all these comic-book adaptations always insist they won’t come back for more unless the sequels can top the originals. The “Fantastic Four” gang has managed to outdo itself the second time around — and still make a bad movie.

“Fantastic Four: Rise of the Silver Surfer” exceeds the first movie mainly by the less-is-more approach. It offers fewer random displays of superpowers that characterized its predecessor, keeping the action brisk and the running time 15 minutes shorter.

That makes it less of a fantastic bore than 2005’s “Fantastic Four,” which became a commercial hit despite cheesy action and effects and dysfunctional infighting among its quartet of superheroes.

The first flick suffered from a miserly story, pitting the four astronauts-turned-mutated-heroes against one another in a sort of silly sibling rivalry, then tossing in an aimless megalomaniac whose only goal was destroying the good guys.

This time out, the heroes have their act together, if not their acting — the performances are still as stiff, thin and brittle as the paper their Marvel Comics source material was printed on.

There’s a little more at stake in “Silver Surfer” — the destruction of Earth — though even that impending doom sometimes takes a back seat to the goofy interpersonal crises of the Fantastic Four.

Our heroes all return with the powers they gained in the first film: Brainiac leader of the pack Reed Richards (Ioan Gruffudd), whose elasticity allows him to bend and stretch into any shape he wants; Sue Storm (Jessica Alba), who can make herself invisible and project force fields; her brother, Johnny Storm (Chris Evans), able to fly and burst into flames; and Ben Grimm (Michael Chiklis), a super-strong rocklike hulk.

Also back is director Tim Story, who has learned a thing or four about action since last time — “Silver Surfer” shows definite improvement over the choppy fight sequences in the first movie.

Their superhero cover blown in part one, the Fantastic Four are caught in a tabloid-TV spectacle as Reed and Sue’s wedding approaches.

The arrival of an interstellar harbinger of doom, the Silver Surfer, interrupts the nuptials and forces the Fantastic Four into reluctant alliance with their archenemy, Victor Von Doom (Julian McMahon), who has metallic and electromagnetic powers and in some conveniently unexplained manner has returned from apparent destruction in the previous flick.

The Surfer rides into town on a silvery surfboard, blasting craters around the planet, freezing entire seas and otherwise making a nuisance of himself. We gradually learn he’s not the big cheese, though; surfer boy is just the advance man, leading a hungry entity known as Galactus to planets it can devour.

To its credit, “Silver Surfer” flows by quickly, if brainlessly. The dialogue from screenwriters Don Payne and Mark Frost is so shallow it provokes unintended laughs (“Your encounter with the Surfer has affected your molecules,” Reed informs Johnny, proving that not all eggheads have a way with big words).

Amid all the vapid dialogue and visual fireworks, the performances seem like afterthoughts, particularly those of Gruffudd and Alba, who could use a snap of the fingers by fiery Johnny to light a spark of personality within them.

The cast also includes Kerry Washington, returning as Ben’s sweet, blind girlfriend; and Andre Braugher, stuck in a bad Patton act as an Army general who enlists the help of the Fantastic Four.

The Silver Surfer looks like the shape-shifting cyborg of “Terminator 2: Judgment Day” in his smooth, shiny transition modes. Though Story and his crew were aiming to emulate the character’s appearance in the comics, there’s not much room for expressiveness in a featureless creature that resembles a shopping-mall mannequin.

Droopy vocals for the Surfer by Laurence Fishburne don’t help, either. He’s got energy enough to punch massive holes across the globe, but the Surfer sounds as though he can barely keep awake.

Like the first movie, the sequel closes with an image that could be a nugget for another installment. If the really bad first chapter can pack in enough fans to warrant a sequel, there’s no reason why the merely bad second one cannot do the same.

“Fantastic Four: Rise of the Silver Surfer” is rated PG for sequences of action violence, some mild language and innuendo. Running time: 92 minutes. One and a half stars out of four.