"Nobody knows anything" was what the Hollywood screenwriter William Goldman wrote about the people who make movies. Unfortunately for us, the same can't be said for the people who watch them: when we sit down in front of a big-budget blockbuster we tend to know what we're in for. Worse, when the film is part of a franchise – arguably Hollywood cinema in its most distilled form – we're there because we know what we're in for; in fact, we can predict more or less exactly how the next two hours will play out, right down to the finest details.

Which brings us to the Alien franchise, a series of films that doesn't so much defy expectations as seal them in an airlocked escape pod and blast them into the depths of space. Rather than doubling down on what came before, each Alien movie is helmed by a new director with their own deranged and distinctive vision. The result is a series comprised of standalone genre movies – slasher movie, action flick, film noir, fantastical drama – and one that is entirely unique in Hollywood cinema.

Given that we go to the cinema to be told a story, it seems odd that so many of the films we flock to are notable mainly for their rigid predictability. From the makers' point of view, though, it makes perfect sense. If the aim of a franchise is to sell tickets, then what better way to do so than to guarantee another slice of what was so popular last time round?

Without fail, a Fast and the Furious movie will end with a cheerfully ludicrous, nitrous oxide-fuelled action sequence before decamping to Vin Diesel's back yard to hear him ruminate warmly on the importance of family. James Bond will charm the girl, foil the villain's masterplan and brutally murder him while delivering a pithy one-liner about the nature of his death. Rocky Balboa will bag a title fight, train gruellingly (probably in the outdoors, definitely to lame music) and take a beating in the ring. He may or may not win, but his eventual moral victory is in no doubt at all.

In Scott's eye, rather than cure the oppressive ills of earthbound capitalism, space travel would merely compound them: our heroes, blue-collar workers for a giant mining corporation, spend the opening act grumbling about their bonuses, the tedium of their jobs and the tight-fistedness of the suits back home. When the alien does arrive, it's not one of Close Encounters' dazed martians or Star Wars' cuddly weirdos: it's a blood-soaked penis, fanged and erect, which erupts from the chest of a central character before scuttling off to grow at a frightening rate into a clanking monster.

The original film was released in the summer of 1979 – ten years after Neil Armstrong first walked on the moon – and came at a time when Hollywood's visions of outer space were loaded with hope and optimism_. 2001: A Space Odyssey_, Star Wars and Close Encounters of the Third Kind had all been box-office show-stoppers in the previous decade, all movies that reflected space-age dreams of euphoric self-discovery, utopian progress and infinite horizons. Then along came Ridley Scott, and suddenly outer space was cold, claustrophobic and chock-a-block with gruesome phallic symbolism.

Cameron had written the screenplay for Rambo: First Blood the year before and, like that and pretty much every Hollywood action flick of the Reagan era, Aliens was a thinly veiled excuse to re-enact Vietnam on the big screen, the savagery of the enemy fully accentuated, faceless adversaries being slaughtered in their droves and the war's outcome conveniently readjusted. The result was a deliriously gung-ho gore-fest that raised the bar for mainstream action cinema for decades to come.

Like any sequel, some serious ramping up was done – a lone predatory enemy became thousands of them, as our platoon of heroes do battle with them on their planet – but that was the only concession to convention: apart from the creature with the bulging, elongated head (there's that imagery again) and Sigourney Weaver's hero Ripley, Aliens was unrecognisable from its predecessor. Instead of a pared-back slasher film, this was a vast and buccaneering shoot-em-up. Cold sweat had been replaced by hot, crackling popcorn.

Alien wore all the bells and whistles of sci-fi, but it was really a horror movie in fancy dress: the story of a blade-wielding lunatic hiding in the dark, picking off a gang of dimwits one by one before being outwitted by the final girl. So no real surprise, then, in an age of Freddie Kruger and Michael Myers, that it soon spawned a sequel. Except Aliens was a sequel in name only: Ridley Scott was out, James Cameron was in, and slow-burn adult terror was traded in for high-octane, gloriously adolescent blockbuster.

It also built on the first film's feminist undertones and hints of maternal dread, throwing both centre-stage. While Alien gave us a female slasher protagonist who had no romantic interest and went largely un-sexualised, Aliens turned Ripley into a proper, armed-to-the-teeth action hero – paving the way for Sarah Connor, Buffy, and Imperator Furiosa and countless others. And while Alien kept its themes of motherhood implicit with its womb-like spaceship interiors and the creature's means of appearance (first hatching from an egg, then bursting violently from a human stomach), Aliens introduced a traumatised 10-year-old daughter figure for Ripley to rescue, protect and effectively adopt.

Six years and innumerable hired-and-fired screenwriters later came Alien 3, a bleak mediation on death and nihilism that couldn't be much further from Cameron's souped-up crowdpleaser if it tried. The second sequel made it to screens after a long and tormented production history, and landed to a middling reception. Watching it back now, it's hard not to think much of its intrigue went unnoticed at the time: David Fincher, who would go on to direct Fight Club and the Social Network, was making his directorial debut and essentially trials a beta version of what would become his signature style – all murky interiors and disorientating close-ups – and the plot device of throwing Ripley in among a prison colony of sex offenders is a bold twist on the threat of rape, which had loitered in the background in previous films.

It's hardly a movie short on ambition: there are notions of redemption, sacrifice, existentialism and the horror of motherhood all at play, with Ripley's character even going full Christ-figure in the end. It's weird, and not exactly wonderful, but it's certainly never boring.

By the time Alien: Resurrection came round in 1997, the series' determination to start anew each time had almost become its defining feature. So it was oddly logical that the austere gloom of David Fincher's world was followed by the bizarre stylings of French fabulist Jean-Pierre Jeunet. If Alien 3 was notable for how it meandered off on intriguing but unsolvable tangents, Alien: Resurrection took the same ill-disciplined baton and ran for the hills, making Ripley an uncanny human/alien hybrid and peppering the action with moments of absurdist humour and grotesque visuals (notably when a cloned and resurrected Sigourney Weaver gets to wander around a laboratory filled with failed and deformed versions of herself). It doesn't all work, and at times can seem a bit of a mess. But at least it's a mess that comes with enterprise, vision and yet more phallic metaphors, all filtered through a loopy French imagination.