Prowling back and forth across the U.S.-Mexico border, stirring up dread, Denis Villeneuve’s drug-war-quagmire movie puts on very serious airs. It stars Emily Blunt as an FBI agent increasingly dismayed by cartel brutality, Josh Brolin as a shady federal operator who extends her a dubious opportunity, and Benicio Del Toro as a frightening embodiment of the dubiousness. Sicario skillfully exudes the aura of realism, of professionals at work. No mere action flick, this — it seems at first like a high-minded film made with major resources, including the inside knowledge of special advisors. And yet Villeneuve’s insistent solemnity isn’t wholly convincing; the basic thriller mandate eventually takes precedence. So it’s not as forceful an exposé as the documentary Cartel Land, from earlier this year, or for that matter the 2010 documentary El Sicario, Room 164, in which a hooded hitman sits in a hotel room recounting 20 years’ worth of torture and murder. Villeneuve’s film, written by Taylor Sheridan, pays off its suspense with fierce violence, and seems therefore sensational — it can’t quite transcend being an array of set pieces, haunting though they are. Haunting? Tragic? Badass? With Blunt as sharp and expressive and easy to root for as ever, Brolin and Del Toro don’t romanticize their characters, but unfortunately some viewers will.