"Something is coming," a young boy whispers to his assembled friends. "Something hungry for blood." It's 1983 - or 2016 - and you're in Hawkins, Indiana - or on your sofa - playing Dungeons & Dragons... or watching Netflix's Stranger Things. Over the decade since we first encountered the youthful protagonists, the show, created by the Duffer Brothers, has become an international sensation, launching careers and spawning an empire of video games, novelisations, podcasts and a stage play. Now, it ends where it began, with one last roll of the dice for our intrepid players.

With the entire world imperilled by the conquest of Vecna (Jamie Campbell-Bower), the gang execute their final, desperate plan. Eleven (Millie Bobby Brown) will head into the Abyss, team up with Max (Sadie Sink) and attempt to inveigle Vecna's vessels - the kidnapped children, including Holly Wheeler (Nell Fisher) - out of his psychic prison. If they can do this, they might be able to set up a final showdown with Upside Down's dark overlord - one where El will need all the help she can get. "One last fight," Mike tells his compadres, "and this whole nightmare, it'll be over." And so off they trot, on a patience-testing feature-length finale that will take them into the belly of the beast - and viewers into the bowels of befuddlement.

This final season of Stranger Things, arriving after a three-year hiatus, has felt burdened with a lot of responsibilities. The actors have (largely) moved on to other projects and aged out of their roles, and it's clear that the protracted story needed wrapping up. But the show is still Netflix's most important original IP, and its conclusion a chance to distract from a disappointing year (creatively). Yet the final season has received a mixed response, as the tangle of narrative threads starts to obscure the show's famously zingy chemistry. "We're like Dorothy in Oz," Max laments, "except there's no Yellow Brick Road." And even with the end in sight, the show is perilously confusing. What exactly is the Upside Down? How does the Abyss function? Why is Vecna using these stolen children? What is the relationship between Henry Creel, the Mind Flayer, Dr Brenner and Eleven? And why did the show cast Linda Hamilton and then only give her about five minutes of screen time?

The plot of this series has left me - like many of the show's fans, according to the internet - baffled. But then again, the great success of Stranger Things has always been its casting, not its writing. Winona Ryder's Joyce was a superb anchor for the show's emotions, yet she has been sidelined this season, with the writers apparently unsure how to integrate her into a more action-based narrative. David Harbour, similarly, was an inspired booking: gruff, broken, but ultimately likeable. And in its young cast, Netflix has picked a few stars: Finn Wolfhard has grown into a charismatic screen presence, Dustin Matarazzo has natural comic timing, and Sink is now a legitimate dramatic actor. (It is hard to avoid the feeling that Netflix is grooming its new young star, Fisher, for a possible spin-off.) In Joe Keery and Maya Hawke (Steve Harrington and Robin Buckley, respectively), it unearthed two plausible A-listers, and perhaps the best piece of later casting was Campbell-Bower - best known for turns in Sweeney Todd and Harry Potter - in the dual role of Vecna and Creel. His performance, in particular, elevates this finale.

It feels a shame, then, that this fifth and final season has deviated so far from the show's established character work, and become just another CGI rock'em sock'em adventure. From normal kids, they've become "interdimensional space travellers". Dustin has gone from a smart lad to a literal astrophysicist; Nancy, from a surprisingly tough prom queen to an Ellen Ripley-esque badass. Some of this is character development, but much of it is a consequence of the stakes being raised higher and higher, the threat becoming greater and greater. "They had a lot more to overcome than just puberty," Hopper tells Joyce. No s***. They're now action heroes who can take on kaijus and make the United States military look like Darth Vader's stormtroopers.

In the end, the Duffer Brothers just about manage to right the ship in the final act. There's a degree of fan service to this (Will's coming out scene, in the penultimate episode, was a particularly clunky moment where the discourse seemed to collide with the narrative), but it ensures that each of our central characters - El, Mike, Will, Dustin, Lucas, Max, Nancy, Jonathan, Steve, Robin, Joyce and Hop - are given a send-off that rounds out their arc. This helps to offset the show's Upside Down denouement, which is interminable, anticlimactic and so confusing that it's hard not to give up on the exposition.

Wormholes, parallel worlds, hive minds, dimensions, portals and rifts. Don't let all this pseudoscientific guff distract from the fact that Stranger Things is, in the end, a show about growing up in a boring town in the middle of nowhere. Matt and Ross Duffer - inspired by The Goonies and ET - have created a coming-of-age saga for the present day. It might have lost its way in a maze of sci-fi bunkum, but it will still influence a generation of viewers in much the same way that, a couple of decades ago, the works of Steven Spielberg inspired two young brothers.

In the end, Stranger Things lost its way in a maze of sci-fi bunkum - review