Despite being a director unafraid to explore a variety of genres, Spielberg has always been best at bringing monsters to the screen. Duel is his first attempt at doing this, and even though the monster here is in vehicular form, echoes of the director's many successes here reverberate through to his later, more well-known works such as Jaws and Jurassic Park. Spielberg effectively and imaginatively transforms the hulking tanker truck into a menacing and memorable behemoth, particularly through his skilled choices of both camera angles and cinematography.
Duel is regularly at its best when focused purely on the truck and its chosen prey, David, played ably by Dennis Weaver. The actor's performance is strong and authentic and especially impressive considering the large amount of time Weaver spends as the only person on screen. Weaver believably sells his character's descent into mental instability and paranoia, questioning his own sanity more and more during the film's first two acts, as well as convincingly building a hero versus nemesis relationship with the truck itself, as well as its perpetually unknown driver. And in terms of pure action, of course, the film offers plenty of entertaining and well-crafted car chases.
Despite its many strengths however, Duel hasn't aged as well as many of Spielberg's other films. The entire scene at Chuck's Diner feels outmoded, hitting the brakes unnecessarily and far too hard after the tense and heart-pounding opening, whilst adding little to the story overall. Spielberg's choice to at times have Weaver deliver David's inner monologue as a voiceover also feels blunt and dated, especially when placed alongside many of the director's more refined choices. The climax too, whilst suitably exciting and adrenaline-fuelled, provides something of a messy and morally dubious conclusion that doesn't satisfy as much as a lot of what has preceded it.
As a directorial debut, however, Duel stands up remarkably well whilst at the same time foreshadowing much of the success Spielberg would have later in his career. It's faults can't be ignored, but they can largely be forgiven due to the simple yet incredibly effective and innovative thrills the director crafts. Duel is the opposite of epic, focusing on a tense and insular story of an average man unwillingly thrown into conflict and danger; it also shows that, even though Spielberg now chooses to surround himself with grand tales, elaborate settings and technical wizardry, he doesn't actually need them to tell a great story.