How do you make a sequel to a cult classic? Is it enough to repeat the key moments of the original, or should you build on them, undercut them, move beyond them altogether? In this belated follow-up to Ridley Scott's revered 1982 Blade Runner, director Denis Villeneuve (Arrival) rises to the challenge, riffing constantly on his source yet holding it at a distance that leaves room for his own independent vision.

The science-fiction premise of Blade Runner, derived from Philip K. Dick's novel Do Androids Dream of Electric Sheep?, gives the enterprise a self-referential twist. The anti-hero Rick Deckard (Harrison Ford) was employed to hunt down androids known as "replicants", imitation people outwardly identical to the real thing.

Fans have long debated whether Rick is a replicant himself, but Blade Runner 2049, set 30 years on in the same dystopian version of Los Angeles, avoids teasing us with an equivalent puzzle. Played by Ryan Gosling with typical forlorn blankness, Deckard's successor Officer K knows all along that he's not human, and that the childhood memories he carries round with him are not his own.

Villeneuve and his writers (including Hampton Fancher, who worked on the original Blade Runner script) share this willingness to take artifice for granted. In one sense, this makes Blade Runner 2049 less of an exercise in nostalgia than Scott's film, which harked back to the 1940s in style - Deckard dressed and behaved like an archetypal private eye - while asking if true feeling might be found even in the midst of falsity and corruption.

Today, cinema has moved on: the drama here isn't about the search for authenticity, but about the relationship between different types of images. Ford as the aged Deckard is the film's most vivid presence and there's paradoxical energy in his weariness, which now seems bone deep. His impact is inseparable from his status as an iconic reminder of cinema's past.

Meanwhile, the video billboards from 2019 LA have evolved into full-fledged holograms, some gigantic, others not unlike K's computer-generated girlfriend Joi (Ana de Armas), whose affection he's willing to accept at face value. Joi's phantom allure is central to the most memorable scene, which recaptures some of the bizarre eroticism of Scott's film while borrowing from Spike Jonze's Her, a sunnier vision of technology triumphant.

One reason Blade Runner has worn so well is that Scott and his collaborators created a future you could dream yourself into, a city assembled from disparate parts - from low-rent noodle shops to buildings styled like ancient temples. Villeneuve does not try to replicate this achievement: Blade Runner 2049 is visually and geographically more fragmented, moving between the dark, rainy city and the barren areas beyond the sprawl.

Even within the city, the crowds have thinned: Villeneuve can mimic Scott's congested textures when he chooses, but instinctively prefers a starker look, using shallow focus to isolate the actors in blurry space. Hints of what lies beyond are conveyed by the soundtrack, often far more atonal and forbidding than the electronic score by Vangelis which was draped over the 1982 Blade Runner like a blanket.

That Villeneuve takes nearly three hours to tell a relatively simple story is one sign of his daring. Like its predecessor, this Blade Runner is a genuine science-fiction art movie, driven by mood and ideas rather than plot. Perhaps it's a symptom of Hollywood's decay that a film about the future should be so wrapped up in the past. In his complex negotiations with a model that remains out of reach, Villeneuve comes closer than Scott ever did to imagining a post-human world.