How far over the top can a movie go? Few have been as flamboyantly absurd as “Shoot ’Em Up,” which is explicitly like a live-action cartoon—though one made with an adult audience in mind. Viscerally exciting but without a brain in its head, it’s stylistically in the tradition of “Running Scared,” “Domino” and “Smokin’ Aces”—which should be enough to tell you whether it’s your cup of comic-book violence or not. But it’s more fun than any of them. It’s more like a third chapter of “Grindhouse,” and there too it’s more enjoyable than that picture’s actual episodes. But not good enough.

The premise: a bunch of nasty hit-men led by a smirking, bloodthirsty madman named Hertz (Paul Giamatti, chewing all the scenery in sight) is dispatched to off an extravagantly pregnant woman (Julian Richings). They catch up with her on a deserted street where a somber, stone-faced fellow called Smith (Clive Owen) intervenes. Pulling a carrot from his pocket, he takes a bite and then uses the rest like a spike to kill one of the attackers before delivering the dead mother’s child as gunfire rages around him.

Smith then becomes the newborn’s protector, taking the child to Donna Quintano (Monica Bellucci), a prostitute who reluctantly agrees to breast-feed the baby (having recently lost her own, she’s still lactating). Investigating the reasons behind the killing, the couple discover that the dead woman was one of several pawns meant to provide a seriously ill politician (Daniel Pilon) with infants from whom bone marrow could be extracted to keep him alive. She’d escaped when the politico’s enemy hired Hertz’s crew to eliminate the senator’s “harem” to derail his presidential bid, which, in a rather lame joke considering the massive firepower on display here, is based on strengthening gun control laws.

The bulk of the movie consists of Hertz setting trap after trap to catch Smith—all to no avail as the mysterious stranger outwits the goons at every turn. The hero’s habit of munching on carrots as the villain grows increasingly infuriated over his failure to finish the job accentuates the movie’s gleeful perversion of the Bugs Bunny-Elmer Fudd formula of the venerable Warner Brothers shorts. And the outlandish choreography of the chain of shootouts that form the meat of the movie—one actually occurs in mid-air among sky-diving foes, another involves a particularly acrobatic car chase—is certainly impressive, from a technical standpoint, and often visually witty (although the fact that a baby is center stage in much of the mayhem may cause some viewers to wince).

And as well staged as the individual action set-pieces are, over the course of nearly ninety minutes they do grow repetitive. By the fourth or fifth confrontation, it certainly begins to look as though the black-garbed guys being mowed down in such numbers by Smith are the same fellows that he killed en masse ten minutes earlier. And the percentage of bons mots among the one-liners spouted by Owen and Giamatti is alarmingly low; most of the throwaway lines provided by writer-director Michael Davis should actually have been thrown away.

As for the stars, Owen does the same steely-eyed shtick he did in “Sin City,” and Giamatti might have thought he was being paid by the smirk and sneer. Bellucci is easy on the eye, but it must be said that her heavy accent leaves some of her dialogue less than clear (though in view of the quality of the writing, that might not be such a bad thing). Peter Pau’s cinematography is impressive in view of the wild gyrations required in the action scenes, and Peter Amundson’s editing keeps the punches coming, abetted by the heavy metal pounding that fills much of the background score.

Individually the set-pieces that fill “Shoot ’Em Up” are very impressive, but they reach the point of diminishing returns over the long haul. The Bugs Bunny cartoons it’s sending up were, after all, five minutes or less. Davis’ movie is like an outstanding ten-minute audition reel repeated nine times. And even for those who really enjoy this sort of stuff, that may seem like too much of a good thing.