THIS is a curio of a quirky movie, a not very romantic comedy thriller with big-name stars who share too few scenes, a director best known for launching the brief American career of a British comedian, and a running time of two hours that feels closer to three.

The stars are blond Adonis Brad Pitt, in Kurt Cobain grunge fatigues, and widescreen-mouthed Julia Roberts, in her first role since she won the Best Actress Oscar for Erin Brockovich - and her bra the best supporting award.

The director is Gore Verbinski, the man who imported the rubbery Lee Evans to lead the slapstick fun and games in MouseHunt.

After the inventive MouseHunt, here is GunHunt, as Pitt heads down Mexico way to retrieve The Mexican, a priceless if cursed antique pistol seemingly as important in local legend as the British-purloined Elgin Marbles are to the Greeks.

Pitt is playing one of his loose-limbed slacker roles, Jerry Welbach, a hapless bagman already in debt to the criminal fraternity and now ordered to do one last mobster job south of the border. By taking it on, albeit reluctantly, he scuppers his girlfriend Samantha's plans to start a new life together in Las Vegas.

Samantha quits, exit stage left for Vegas, pursued by hired assassin Leroy (James Gandolfini, alias mob boss Tony from The Sopranos, with the same Mafia accent but newly goatee-bearded). Old habits die hard, so he kidnaps her, to ensure loser Jerry stays focused and does exactly what he should in Mexico.

Jerry, alas, is a magnet for trouble, a perennial subscriber to Murphy's Law, and so he somehow ends up losing the pistol and his hired car while acquiring a mangy dog, a most unfortunate corpse and the uncomfortably close attention of Mexico's heaviest heavies.

After their initial splitting fireworks, Pitt and Roberts are kept apart rather longer than the movie can afford, and by the time the bickering couple are together again the chemistry formula has been waylaid. In the meantime, they find themselves handling material that veers from light slapstick comedy to Robert Rodriguez violence and Traffic dark intensity. At times, too, The Mexican is not so much a spaghetti western as Spaghetti Hoops western.

The hamster-cheeked Pitt is more at ease with JH Wyman's over-smart, erratic script and Verbinski's ragged direction than the spiky Roberts but both must bow to the charismatic Gandolfini. His gay, highly sensitive hitman is a hit, whereas overall The Mexican is as misfiring as the gun itself.