If you learn nothing else from movies, learn this: Alcoholism by itself is gauche; alcoholism blended with a splash of literary pathos is tragically delicious. So it goes in Shainee Gabel’s “A Love Song for Bobby Long,” an atmosphere-soaked tale of secrets and barflies in which well-read rummies laze about on rotting floorboards, quoting Molière in the smoldering kisses of a New Orleans sunset.

In a moribund, “Leaving Las Vegas” kind of way, it’s sort of romantic. Unfortunately, first-time writer-director Gabel —who adapted the script from the novel by Ronald Everett Capps — proves a bit too idealistic to sustain her own alcohol-infused illusion. Feisty trailer-park tart Pursy Will (Scarlett Johansson from “Ghost World”) arrives in New Orleans with a chip on her shoulder and a head full of hazy childhood memories; within days, her recently deceased mother’s vodka-sucking roommates, Bobby (John Travolta) and Lawson (Gabriel Macht from “Behind Enemy Lines”), have designed an academic regimen to help her pass her GED test.

Jobless derelicts can be so handy to have around. Of course, these aren’t your garden-variety jobless derelicts. Hobbled, wizened Bobby used to be an English professor at Auburn University. Thin, ruminative Lawson was once Bobby’s star student. How they came to reside in co-dependent squalor in Louisiana is the movie’s big mystery, but not one — once revealed — that leads to any sort of satisfying culmination. Of all things, “A Love Song for Bobby Long” tries to be a feel-good salute to rough men and surrogate fathers, “Curly Sue” as adapted by Charles Bukowski.

At once harsh and sentimental, it feels muddled both thematically and narratively. Johansson, as a headstrong young woman haunted by a phantom childhood, continues to ripen as a performer, inspiring the sharpest flavors here. Travolta, as the gone-to-seed, linen-wearing Southern man of letters, is not so good. What at first appears to be a novel role for the actor — enfeebled, threatening, grotesque — ultimately reveals itself as a slightly rumpled version of his angel/martyr/hero in “Michael.” This one just happens to have a hangover.