Various hands have struggled for years to adapt F. Scott Fitzgerald’s 1922 short story, about a man who lives his life backward from old age to infancy, to the screen, but until now they’ve all given up, concluding that it was unfilmable. And as David Fincher’s “The Curious Case of Benjamin Button” demonstrates, they were right. The screenplay by Eric Roth (“Forrest Gump”) retains nothing of the original but the title and the basic premise, and alters even that so make it nearly unrecognizable, either in detail or in emotional effect. The result is Fitzgerald Gumpified, which is not a pretty thing, despite a physical production that spares no expense, technical wizardry or time (the picture runs nearly three hours) to dazzle the senses.

Fitzgerald’s take on the idea was a darkly comic one in which Benjamin, the son of a Baltimore aristocrat, was inexplicably born as a crotchety old man in 1860. He ages backward until he descends into childhood and infancy, but along the way demonstrates that he’s not a very nice person, having difficult relationships with all the members of his family—grandfather, father, son, and especially his wife, whom he loves when she’s older than he but despises as she ages and he grows younger. It’s a brittle piece of work, and while it certainly carries a touch of melancholy, it hasn’t a trace of sentiment.

The story might have made a sharp satire on screen—though any screenwriter would have had a difficult time coping with the physical circumstances of that birth. But Roth didn’t go that route. He simply chucked Fitzgerald’s tone and virtually all of his plot, save for the general idea, which he altered substantially: Benjamin (Brad Pitt, in various stages of makeup and CGI-added bodily parts) is born a wizened, wrinkled child, and as he ages, becomes an old man with a youngster’s mind, growing intellectually as he moves into middle age and then the prime of life. He ends up as an adolescent suffering the dementia of old age, finally descending into infancy.

And Roth invented an entirely new life trajectory for this much-altered oddity. Benjamin is born to a wealthy New Orleans family in the early twentieth century, and his father Thomas (Jason Flemyng), a well-to-do-businessman, abandons the malformed infant at the door of an old-age home after his beloved wife dies in childbirth. Benjamin is unofficially adopted by Queenie (Taraji P. Henson), a black attendant at the home, and is brought up there, making friends with Daisy (Elle Fanning, then Madisen Beaty), a young girl who comes to visit a relative who’s a resident. He also has a series of “youthful” adventures—one involving a high-living African pygmy (Rampai Mohadi)—before becoming friends with raucous tugboat captain Mike (Jared Harris), with whom he goes off to sea, winding up in Russia, where he has an affair with Elizabeth (Tilda Swinton), the unhappy wife of a British diplomat. Their ship also sees action against the Germans in World War II. Thomas will also reappear to reveal himself as Button’s real father.

Then there’s the now prince charmingly handsome Benjamin’s romance with Daisy (now Cate Blanchett), who’s grown into a beautiful ballet dancer who’s appearing in no less than the Broadway company of “Carousel.” His initial approach to her is rebuffed, but after she’s disabled in an accident, they become a passionate, loving couple and have a daughter. But Benjamin worries over how his condition will impact his ability to be a proper husband and father, and decides that self-sacrifice is the best option from the perspective of his wife and daughter.

The entire story, it should be added, is told in a New Orleans hospital by Daisy, now a dying old woman, to her daughter Caroline (Julia Ormond) just as Hurricane Katrina is approaching. And it’s tied to a bookending device about a watchmaker (Elias Koteas) who constructs a clock that runs backward as a memorial to his son, who died in World War I.

All of this is Rothian picaresque, not Fitzgerald’s biting commentary on the stages of life, and like his earlier smash “Gump,” it’s a mixture of sweet sentiment and maudlin sentiment, with a healthy dose of raucous humor and occasional action to jazz up the ordinarily vaguely morose, meditative atmosphere. It’s sumptuously appointed in every respect—the combination of director David Fincher’s lapidary style (a far cry from “Fight Club”), Claudio Miranda’s swooning widescreen cinematography, the unhurried editing by Kirk Baxter and Angus Wall, the lushness of Donald Graham Burt’s production design, Tom Reta’s art direction and Jacqueline West’s costumes, Brian Sipe’s makeup and Eric Barba’s visual effects, and the evocative music by Alexandre Desplat (not one of his more memorable scores, but better than most) makes for a visually mesmerizing experience.

But the warmth of the images doesn’t translate into emotional effect. “Benjamin Button” is a curious case not only in terms of its protagonist’s aging process, but because it doesn’t generate the visceral reaction it’s obviously aiming for: it’s a gorgeously-made would-be tearjerker that leaves the ducts dry because of its extreme artificiality, in both plot and execution.

That extends from the physical production to the acting. Pitt is handicapped by the fact that for much of the film, his face is superimposed on other bodies, so he doesn’t have full range of movement, but even when he’s himself, there’s a passivity and lack of expression that make him a pretty but rather blank receptacle rather than an energized participant. That’s mostly the result of the characterization the script provides him with, but when a young actor replaces him in the last act, the plot actually becomes a more touching experience. Among the others, Henson is exuberant at every stage as Benjamin’s adoptive mother, Flemyng has a few choice moments as his birth father, Mohadi has what amounts to a scene-stealing cameo, and Swinton impresses as an unhappy woman in need of some passion. But Harris overdoes the bluster, and most importantly Blanchett is variable, sometimes capturing the proper tone but often feeling a bit off. Ormond is wasted in a thankless role.

There’s no doubt that “The Curious Case of Benjamin Button” is a masterful technical accomplishment. But its mournful tone lacks the crowd-pleasing effect of a picture like “Gump,” and in the end it comes across as detached and a bit off-putting.

Maybe it would carry greater emotional weight if it were run backwards. Just joking!