With one of the finest ensemble casts on TV, the third season signed off with a leap into the 90s and an episode which crackled with arguments about technology that were really about something much deeper. Warning: spoilers

Coming from AMC, the Don Draper channel, Halt and Catch Fire was launched to an unreasonable assumption that the 80s-set tech drama would be Mad Men with computers. When it immediately became clear that this wouldn’t be the case, media attention evaporated, in effect punishing the show for not being something it had never been never intended to be. But for those of us who have stuck with it, the show has delivered. Totally original, it isn’t the next anything – it’s the first and last Halt and Catch Fire.

After a second season that put the programmer Cameron and the engineer Donna’s business relationship to the fore – a partnership that saw the more nuts-and-bolts Donna’s self-worth slowly diminish as the more creative, intuitive genius Cameron was showered with praise and credit – the third saw the show hit that sweet spot where all the groundwork laid in establishing the characters in previous episodes paid off.

The core players were split up, then mixed and matched, as Cameron avoided Donna’s attempts to expand their fledgling gaming and social network Mutiny, preferring it to evolve incrementally to preserve its perfection; meanwhile, the brilliant computer engineer Gordon sequestered himself under the stairs with his ham radio, sending out messages to ether on his obsolete device. Joe, the show’s (sort-of) Steve Jobs-alike, stayed away for the most part, searching for the next big thing with disastrous, fatal consequences for his new acolyte Ryan. The cast, surely one of TV’s finest ensembles, delivered the drama with deft economy.

Some of the best acting was wordless, such as Cameron’s disintegration after being ousted from Mutiny, stubbornly forcing the board to move against her with their plans to make the company go public; or Donna and Gordon’s marriage falling apart. This collapse started small, with Donna’s casual admission that she hated their camping trips, memories of which Gordon cherished. Soon we saw the distance between them grow to the point where they could share a home but barely converse.

Annabeth Gish (The X-Files, The West Wing) was a fine addition to the cast as Diane Gould, the rich and headstrong businesswoman who buys into Mutiny and provides some nicely grown-up romance with Bos, Mutiny’s mentor and Cameron’s unacknowledged father figure. Gish is the sort of talent this high-quality show easily attracts. When Amy Seimetz (best known to TV viewers for acting in The Killing and Stranger Things as well as directing and writing much of The Girlfriend Experience) appeared in the penultimate episode as “that Michelle woman”, Gordon’s frizzy-permed employee and would-be girlfriend, the reaction is less surprise and more “what kept you?”

Facebook Twitter Pinterest Kerry Bishé as Donna Clark and Mackenzie Davis as Cameron Howe in season three, episode two. Photograph: Tina Rowden/AMC

Things started slow and steady this season, building up a head of steam that delivered jaw-dropping cliffhangers on a weekly basis: Joe’s sabotage of his company by admitting his theft from Gordon. Cameron losing control of Mutiny. Ryan’s suicide after he bought into Joe’s rebellious talk wholesale and released the source code to the anti-virus software, expecting to be hailed a hero but ending up a liability wanted by the feds. Every week a sock in the jaw that made you want to come back for more.

The four-year time jump for the final two episodes felt natural, even though the show has largely been defined by its 80s setting. The 90s were heralded with signifiers such as video dating, foodie bore “Gordo” and Donna’s now totally grungified surly teen daughter, Joanie, as well as a scene at the convention reminding us how much fun it is to dance to the Pixies’ Velouria, a song that seems to have improved with age.

Much had changed. Cameron had spent the time in Tokyo with Tom, the husband she married in secret then followed abroad, working on four installments of the unwinnable Space Bike, her computer game for Atari that girls love and boys seek to improve – the pushy fan offering her a bit of unsolicited “mansprogramming” at her convention signing table. Donna and Gordon had divorced, Donna going corporate, becoming a partner at Diane’s firm and reverting to her maiden name of Emmerson in order to take up more of the precious real estate on the company’s letterheads and signage.

Facebook Twitter Pinterest Scoot McNair as Gordon Clark: sending out messages to ether on his obsolete device. Photograph: Tina Rowden/AMC

Gordon’s still managing his incurable medical condition, his brain slowly deteriorating thanks to exposure to the toxic chemicals his tech work exposed him to, and seemingly taking a relaxed approach to his successful business. Joe is running a consultancy business from home, a job that appears to consist of him repeatedly saying “no” to clients on his cutting-edge phone headset. Bos is retired, good for him but unfortunate for the finale as he is sidelined repairing his boat; his one scene with Cameron still managed to shine and had one of the night’s few, brief moments of genuine warmth. Another loss was the Mutiny team, the unruly army of Nerf gun-wielding programmers and coders who often provided a geek chorus to the main drama.

It ended, bravely, with a bottle episode, cutting away all distractions by placing the core players in the derelict Mutiny warehouse office. It delivered some classic Halt And Catch Fire moves, tech arguments that were really about personal issues, heavy metaphors made light by the skilled performances.

It turns out Donna might have been the show’s villain, with Kerry Bishé’s considerable charm and acting chops providing a smokescreen. Looking back, Donna has never managed to get ahead without ruining things for someone else, another example of how the show manages to hide things in plain sight – let’s not forget Cameron was pushed out of the company she led, a company called ... Mutiny. That’s two years of signposting an event that was still a huge shock when it happened – it’s hard to think of another show getting away with that. Then there was Joe and Tom butting heads over HTML and HTTP when they were clearly arguing about Cameron. Or having them all discuss how the various internet firms can’t work with each other, a blatant metaphor for the characters themselves.

This 10-episode run was written to be the last; the season finale was supposed to be the end of the entire story. It could easily have been a satisfactory capper to things, with the trio of Cameron, Joe and Gordon all huddled around a terminal, exploring the endless possibilities of a new startup. Leaving them at a stage where their new business is unpolluted and perfect would have been a deserved kindness. But fate – or rather AMC – had other plans and a last-minute reprieve came just last week when a fourth and final season was ordered. AMC knows the show is something special; so do we. So why doesn’t everyone else?