It has taken 25 years, three cinema edits and possibly a round trip to Mars for Ridley Scott to arrive in Venice with the definitive version of his sci-fi masterpiece Blade Runner.

Yet after all this time travel and fine tuning there is still no definitive answer to the burning question: Does Harrison Ford dream of electric sheep?

The glum supercop with an uncanny talent for hunting down rogue replicants - crazed androids to you and me - gives even less of himself away in The Final Cut, which received its world premiere at the Venice Film Festival at the weekend, than he did in the 1982 original.

There is no rambling voiceover by Ford, which the film’s distributors, Warner Bros, originally insisted on for the hard-of-thinking. Here Rick Deckard keeps his thoughts to himself and is infinitely more interesting for it.

This simple conceit makes the film a colder and lonelier place. It was always ravishingly dark. Scott’s vision of Los Angeles in 2019 is the ultimate movie dystopia: a fabulous hell of skyscrapers and monolithic Fritz Lang factories. The sky is cluttered with fuming aircraft and floating neon adverts. It never stops raining on the cramped and seedy streets, and everyone, apart from Ford, smokes like a chimney.

What does it mean to be human in such a diseased world? This is the thrust of Scott’s film noir, which has aged quite brilliantly.

If anything, this remastered version (which will be released on DVD this year) is a far more bitter watch. The differences between Deckard and the six genetically engineered fugitives that he is hired to terminate are less easy to define. The brutal quest by the replicants to inflict revenge on the humans who invented them has been tightened. New links make better sense of Deckard's bruising encounters, notably with Joanna Cassidy’s pneumatic snake charmer and Rutger Hauer’s majestic and psychotic Aryan leader.

But the true value of this version is to sharpen our doubts about the flawed hero. The young Ford is magnetic as the cruel lead, and Scott supplies fresh and sensational evidence that he may not be all he seems. The director boldly inserts a creamy black-and-white dream sequence featuring a unicorn galloping through woodland that is so wildly removed from Deckard’s own reality that he wakes up in a sweat. Might this be evidence of an artificial memory?

The poisonous suspicion adds a terrific edge to the relationship between Ford’s haunted cop and Sean Young’s melancholic replicant, Rachael. The chemistry is alarming and desperate rather than romantic.

The happy ending in the 1982 version, where the couple are seen speeding north in a car through forests towards a new life, has been axed by the director. The future in The Final Cut is far bleaker.

Indeed, if Scott is to be believed, the entire future of cinematic science fiction is already doomed. He astonished Venice last week when he declared that the genre was now as outmoded as the Western.

Utter nonsense, of course. But if that means he will stop tinkering with this stunning, seminal film then we ought to be grateful.

Editor's choice

• The 100 Best Films of the Decade
• 70 facts you didn't know about Marvel
• The 50 Biggest Movies Of 2010