Saturday Night Live's very first episode is brought to life in a gleeful, slightly deranged film with plenty of celebrity cameos

It might seem difficult to imagine that Saturday Night Live — the cultural behemoth now regularly derided for its turgid punchlines and bloodless gags — was once one of the most risqué, risky events on television.

So it was when it premiered in 1975 with a cast of practically unknown comics performing sketches that were, by turns, nutty, absurdist, countercultural and borderline hostile.

A New Yorker review published a few months after the show's debut called it a "huge, darkened, lively TV cabaret" and a welcome alternative to the anodyne "rituals of mass-entertainment television".

Rolling Stone went even further. "The audacity of its concept and execution," wrote an early critic, "alter not so much the visual and audio centres as the central nervous system itself."

The mania and the mayhem, the terror and the transgression: these are the stakes that Jason Reitman attempts to re-create in Saturday Night.

The film, though, faces the same problem that dogs its protagonist: the search for meaning.

Set over one madcap evening in the lead-up to the show's first broadcast, Saturday Night relishes the discomfort of a young Lorne Michaels (The Fabelmans' Gabriel LaBelle), squirming as he's interrogated again and again by producers, peers and studio bigwigs.

The question is the same each time: just what is this thing he's created?

Michaels struggles to answer, though there's no shortage of suggestions. It's a "variety spectacular," says a network staffer selling the show to confused passers-by. Another character calls it "a three-hour sketch comedy revue".

Or maybe it's something entirely less tangible.

"It's postmodern, it's Warhol, it's iconic," offers Rosie Shuster (Bottoms' Rachel Sennott), Michaels's co-conspirator and wife, gazing upon a stage full of bee costumes.

Young Michaels is far from his contemporary persona as the grizzled industry Svengali. LaBelle plays him both nervy and fusty, somehow simultaneously, with his sweater vest threatening to burst with a flurry of butterflies at any given catastrophe.

And catastrophes abound. As the clock ticks ever more ominously towards 11:30pm, the antics heighten: a sofa bursts aflame; a lighting rig comes crashing down in a wild kaboom; a puritanical network censor promises to strike every not-so-PG one-liner.

To make things worse, they're haemorrhaging money like it's payday, the execs are breathing down their necks, and a leading man has just gone AWOL. What's a guy to do?

These hijinks are certainly suffused with a deranged glee – as are the sheer feats of casting here.

Alongside recent breakout stars LaBelle and Sennott, we see Cooper Hoffman (Licorice Pizza) as a gormless NBC advisor, Cory Michael Smith (May December) as the all-American star Chevy Chase, and Nicholas Braun (Succession) in double duty as gonzo provocateur Andy Kaufman and puppetmaster Jim Henson.

It's an ensemble comprising Hollywood's pluckiest upstarts – a canny decision, given Saturday Night Live's own kingmaking legacy.

But their performances can often feel like cosplay rather than true characterisation. Despite the film's painstaking efforts to transform its actors into their real-life counterparts – a hair piece here, a moustache there – we glean precious little about the interiority of these figures.

Indeed, Saturday Night is so invested in reproducing reality that it seems curiously disinterested in actually understanding it.

By no means is it the wittiest account of NBC's hallowed hallways; its walking-and-talking executives and hapless page boys, its peacocking stars and green room conniptions. That would be 30 Rock.

Nor is Saturday Night – despite its pinwheeling camera work and blathering density – the giddiest backstage drama that reveals the lunacy always, always looming behind the spectacle. That dubious honour would belong to Birdman.

Instead, Reitman's film is so besotted with the mythology of SNL that it is difficult to pinpoint exactly what it wants to say.

It's part-historical archive, part-biopic, and part-Easter egg hunt for comedy diehards.

It's also, perhaps, personal wish fulfilment for Reitman, who has said that working on SNL was a lifelong dream – one he achieved as a guest writer in 2008, shortly after making his Oscar-winning film Juno.

Saturday Night, as a result, can veer towards self-indulgence.

There's only so much tension Reitman can sustain when he's hurtling towards a foregone conclusion.

Unlike the thrilling gamble of SNL's debut, we know how this story ends – with Michaels pulling it off. Seeing precisely how it happens can feel trivial.

Saturday Night is in cinemas from October 31.