You would think I’d have learned by now: Never trust trailers. They made Wong Kar Wai’s arthouse “2046” look like a chick flick. They are the reason people keep paying to see Nicholas Cage act.

Australian noob Andrew Dominik’s second film, “The Assassination of Jesse James by the Coward Robert Ford,” should not have come as a surprise. The trailer would lead you to believe that “Assassination” follows train-robbing desperado Jesse James through his last days of gunslinging, which culminates in a final showdown between James and his arch nemesis — that dastardly coward, Robert Ford. Don’t get me wrong; I’m glad the film didn’t turn out that way. But I wish I hadn’t prepared for nearly three hours of it. Instead, the film is a sluggish, artful approach to the Western, much in the same way that “Brokeback Mountain” is a Western, offering more reflection on the genre than actually embodying it. The homoerotic tension is a just a welcome bonus.

“Assassination” opens as a portrait piece, a narrated catalogue of the legendary Jesse James, with whom the film is surprisingly less concerned than the title would suggest. During what would be his last train robbery, Jesse meets 19-year-old devotee Robert Ford, played by an eerily subtle Casey Affleck — comparable to close friend Matt Damon in “The Talented Mr. Ripley.” The next two hours witness the slow unraveling between the James and Ford boys, which plays very much like a sepia photograph.

And just like a turn-of-the-century daguerreotype, Dominik’s apparatus is unmoving and composed — an uncanny visual perfectionism. The intentional vignetting — actually a technical term that refers to a lens that blurs the edges of the screen, but here doubles as a literal term to describe the film’s episodic quality — gives the film an ingress to a more artful cinema.

When I heard that Brad Pitt had won the Volpi Cup for his performance in the title role, I had hopes for a return to his Golden Years — that bold streak of movies around the mid-to-late 90s that hit a wall with his 2001 trifle, “The Mexican.” Since then, he has appeared only in fleeting images of bad movies and whipped husbandry. And I hardly think “Assassination” is much of a comeback (I was selfishly waiting for Robert Ford to realize that he actually *was* Jesse James, but alas …). Pitt’s acting isn’t as big a problem as the role. While he manages to pull off some of the amateurish dialogue, his limited direction under Dominik doesn’t hold up against the long, transposable scenes of the film (the much-anticipated 2006 release was postponed due to several re-edits). The actors suffer because Dominick lacks the savvy to fill this three-hour vacuum, and at times even the actors themselves seem disentranced with the world he has created. Boring I can take, but empty is another thing altogether.

For a freshman director, though, Dominik does enough things right to make the film worth sitting through. Even while he adorns his film with too-obvious dialogue and visual metaphor, he manages to capture a conflicted past with the wistful quality of a daydream. There’s no buildup — you know what’s coming, and curiously so does James — so instead you appreciate the relationship between the men, who fasten themselves into a forced closeness, in an all-male world of outlaws where weapon and manhood are interchangeable. That explains why Jack and Ennis never robbed a train.