The Outer Limits is usually regarded as being in the shadow of its more popular predecessor The Twilight Zone. While it did ape TZ's format, it was still a format that regularly struck gold: get the best writers and actors you can and knock out a different, richly imaginative story every week. In fact, it did this so well that many an argument has broken out over which story belonged to which show.

The Outer Limits is that rare thing: a knock-off that often equalled what it was knocking off. That even goes for its eerie introduction. "There is nothing wrong with your television set," says a voice, as the screen goes through flickering convulsions. "Do not attempt to adjust the picture. We are controlling transmission."

The Outer Limits may not have had a visionary like TZ's Rod Serling at the helm – but it did, for the first season at least, have Joseph Stefano, who was no slouch. He joined the show after adapting Robert Bloch's 1959 novel Psycho for Hitchcock, and his subsequent TV commitments meant that he had to turn down opportunities to script The Birds and Marnie.

Stefano toned down the supernatural elements that were so common in TZ and upped the science fiction. The Outer Limits offers monsters and adventure, but its stories are more like mysteries than morality plays. In A Feasibility Study, an entire town is scooped up by aliens who, it emerges, are planning an invasion; in The Probe, survivors of a plane crash awake to find themselves en route to another world on an automated spaceship. It slowly dawns on them that they are unlikely to survive.

The show is full of familiar faces: plenty of its actors went on to greater things. Leonard Nimoy stars in I, Robot, about a beautifully designed android put on trial for murder. "Now wait a minute," says a stunned local. "Are you telling me that Sheriff Barclay arrested a mechanical man?" Fellow Trekker William Shatner and David McCallum appears in the series, too, as do Robert Duvall and Bruce Dern, who is pitted against ant-like aliens the size of rats in The Zanti Misfits. They have demonic, humanoid faces and want to turn a town in California into a penal colony for their undesirables. It sounds like just another B-movie, but the opening narration takes it somewhere else. "Throughout history," it runs, "compassionate minds have pondered the dark and disturbing question: what is society to do with those members who are a threat to society?"

There were only two seasons of The Outer Limits, running from 1963 to 1965, but its influence is still felt today. Some see echoes of The Architects of Fear episode in Alan Moore's graphic novel Watchmen, while a lawsuit was threatened on behalf of writer Harlan Ellison when James Cameron's The Terminator showed similarities to his Outer Limits episode Soldier. That's why Ellison now has a credit on Cameron's movie.

Ellison's other contribution to the series is Demon With a Glass Hand, which stars Robert Culp as an anmesiac who pieces together his identity by locating the fingers missing from his robotic hand. Along the way, he learns not only that he's from 1,000 years in the future, but also realises he knows the location of the missing population of the Earth. The story was meant to be a globe-trotting chase, but the budget restricted it to one large LA building and it's all the better for it. Like many Outer Limits episodes, it's a tense, thought-provoking mystery that will stick in your brain for decades to come.