When “Erin Brokovich” hit theaters last February, more than a few critics concluded that director Stephen Soderbergh, the indie demi-god behind sex, lies, and videotape, had finally sold out, abandoning artistry for security.

Soderbergh’s follow-up was typically idiosyncratic; rather than making another genre film, he created a genre. “Traffic” might be best described as the first epic-thriller, combining the length and scope of the former with the tight construction and relentless pacing of the latter. The film nevers flags for a single minute of its two-and-a-half-hour running time, due in no small part to the fact that it serves up a significant plot twist in nearly every scene.

Despite 110 speaking roles, more than 10 major characters and half a dozen interlocking subplots, “Traffic” never feels ponderous or incoherent. Plot threads thicken and intersect, producing crescendoes of startling violence and spectacular narrative complexity.

Soderbergh’s skillful use of handheld cameras, showcased in his masterful but little-seen “The Limey,” should make him the envy of every Dogme 95 auteur. The jerky camera movements never allow for a moment’s ease, denying the possibility of a distanced observer who could make sense of the chaos that unfolds in front of the lens. Instead, the mood is one of dreadfully punctuated monotony and of muted but unending panic, where violent death can occur at a moment’s notice.

Refusing to allow his audience shelter in the stylistic conventions of suspense film, Soderbergh never uses music or flamboyant visual tricks to amplify suspense, instead relying on silence, both literal and figurative, to underline the sense of constant dread. The film’s first shootout begins without the slightest warning; the second takes place with no sound at all.

A sort of absurdist fatalism hovers over these bursts of violence, in which friend and foe prove indistinguishable. Soderbergh’s conspicuous directorial restraint suggests that all the participants are doomed agents of forces beyond their control; who lives and who dies is simply a matter of chance.

A masterpiece of visual storytelling, “Traffic” offers unremitting suspense, a showcase for an enormously gifted ensemble cast and precious little insight. For all the talent on screen and behind the camera, the film falls victim to the tension between the demands of a thriller and its longing for social and political significance.

The film’s strongest scenes depict the struggles of a conscientious Tijuana cop (Benicio Del Toro) to maintain his integrity in a situation where honesty is a route to a shallow grave. The Mexican scenes unfold in Spanish, captured in a grainy sepia monochrome that smacks of futility and squalor. These scenes, pivoting around Del Toro’s haunting performance, assemble a genuinely shocking picture of near-universal corruption.

Soderbergh is equally successful in chronicling the thankless tasks of two low-level DEA agents (memorably played by Don Cheadle and Luis Guzman) and rendering a suburban teenager’s descent into addiction in scenes that are chilling yet devoid of sensationalism.

Two of the other narrative threads involve “civilians” like the expectant mother (Catherine Zeta-Jones) who discovers her husband is a drug kingpin when he is arrested, leaving her to fend for herself. These stories might be described as drug war fables, relying as they do on highly contrived scenarios to generate trite homilies about the futility of the war on drugs.

While the ironic and improbable twists of these stories make for a consistently gripping thriller, they also sabotage the film’s credibility and undermine the authority of its conclusions. Gaghan’s hamfisted flailing for moral ambiguity and sophistication makes the film seem more simple-minded than it otherwise would have been. Since the film articulates its thesis in the most contrived of its episodes and in so clumsy a fashion, its arguments fall flat.

The film’s most relentlessly didactic plot thread deals with the newly appointed drug czar (Michael Douglas) who learns the true perils of the war on drugs when his daughter (Erika Christensen) becomes an addict. The Douglas character is so hopelessly na•ve that he needs constant instruction on the realities of the narcotics trade from a series of minor characters, allowing Gaghan to lecture directly to the viewer on why U.S. efforts to stop the flow of drugs are doomed to failure.

Douglas is such a dramatic straw man that his eventual realizations seem obvious or forced. Despite the powerful performances and Soderbergh’s subtly harrowing depiction of a descent into addiction, the entire subplot feels dated, a superlative rendering of a two decade-old TV movie of the week.

As a result, the thesis that Soderbergh and Gaghan present does not jive with the conclusions viewers derive from watching the film. The film thinks it constitutes an argument against the war on drugs, but it bases those arguments on scenes that simply serve as vehicles for lectures and cheap ironies.

As a thriller, “Traffic” celebrates the perseverance of a few honest cops against hierarchies of ruthless criminals. The viewer leaves the movie not wanting to see the war abandoned but won, a desire which Soderbergh and Gaghan have unwittingly amplified. Instead of being intriguingly ambiguous, “Traffic” seems confused and dissonant, as if the filmmakers had failed to understand the implications of the story they tell.

You leave the film wishing that Soderbergh’s talent for understatement had extended to the script, that the film’s technical brilliance didn’t mask so shallow a premise. Ultimately, “Traffic” is as exhilarating as it is intellectually narcotic. It’s a trip unlike any you’ll ever have, but one worth taking with a grain of salt.