For the last day or so, Twitter and social media have been reverberating with the aftershock suffered and enjoyed by fans of Game Of Thrones. I shan't go into the events that caused grown people to writhe in their sofas, gasp huge draughts of air and unleash a collective, "What the - what the FUCK??" that resounded on both sides of the Atlantic as the penultimate episode of the third series wound up to its astonishing conclusion. Aficionados will be well aware of what happened at the Red Wedding, others hissing about "spoilers", still others have no idea what all this means, and why it should have elicited responses of this variety, as if it what was happening was important, like the football, or something.

Game Of Thrones could be said to be a sequence of such jaw-dropping, breath-suspending, hands-to-mouth moments. Its creator George R R Martin, author of the novels on which the series is based and heavily involved in its small screen adaptation, is a master of setting up and unleashing such set piece events, whose impact on the viewer is as sensational as the sudden collapse of a civilisation. More of that later, however. The lavishly budgeted show, set across the globe of an imaginary, medieval-style world and filmed in similarly planet-straddling locations, has dedicated message boards and fan sites, with most journals offering a recap service on which fans can ruminate and reflect on the latest series. They are well catered for.

However, there is also a significantly large body of individuals who are conscious of all of the fuss, wondering what it's all about, but more wondering how on earth friends they supposed to be members of the intelligentsia could be caught up in what appears to them to be a Tolkienesque fantasia, a spurious never-neverland of swords, sorcery and dragons, in which the House of Targ slugs it out against the Kingdom of Yanchester while over the sea the Carthaminions lay siege to the golden city of Darma Sutra, or somesuch. Surely this is the stuff of adolescent escapism, they suspect, a televisual, head-in-the-sands opiate for the masses in troubled times. For various reasons, they will not test their suspicions by actually watching the programme. Too much to catch up on. Better things to do. Broadcast on a Murdoch channel.

I say all this because I was one such sceptic. Never bothered with Lord Of The Rings, gave Star Wars a wide berth, disdained Dungeons & Dragons, and on hearing the word "epic" was liable to reach for my Mike Leigh box set. It took some persuading to get me to watch the first series. Having done so, however, like millions of others, I was almost immediately transfixed and immersed.

There's barely space to go into the vast and complex web of dramatic doings and personae that comprise Game Of Thrones, so vast that even those obsessed with the show sometimes struggle to grasp who's who and what's going on. Suffice to say that it tells the story of an ongoing power struggle, a civil war to lay claim to the contested iron throne of the Seven Kingdoms of Westeros, set in the sumptuous, Southern location of Kings Landing. It's currently held by the Lannisters, with the odious young Joffrey in the chair, bastard son of his mother Cersei following an incestuous liaison with her brother Jaime. However, following Jaime's summary defenestration of a young member of their family from a tower window, who catches him at it with Cersei, a chain of events is set in place that pits the Northern Starks, headed by Sean Bean as patriarch Ned, against the Lannisters, who are directed with cool martial expertise by Joffrey's grandfather Tywin (Charles Dance). Meanwhile, Stannis, brother of the late King Robert Baratheon, insists he is rightful heir to the throne, his efforts assisted by a seductive sorceress and culminating in a spectacular siege at King's Landing, one of the show's greatest set pieces. And then, in hotter climes across the Narrow Sea is Daenerys, exiled daughter of the King defeated by Baratheon, who, with the assistance of young dragons supposed to be long extinct, is slowly trekking her way across land, sacking city by city, to lay her own claim to supremacy.

With transportation limited to horseback and trundling wagons, and movement across country slow, the plot is allowed to move at a luxuriantly glacial pace, series after series. Many of the show's key characters, such as the Stark daughter Arya, her brother Bran and Jaime are involved in long treks back to some uncertain destination, having been forced to flee and scatter by seismic events. This allows for lengthy sub-plots, individual odysseys which are engrossing stories in their own right, involving flashpoints, clashes and revelations which make Game Of Thrones fascinating at myriad micro-levels.

All of this might make the programme seem onerously baroque and too much of a claim on your attention. However, although aspects of the series are appropriately, if spectacularly far-fetched, it works because it is grounded in the brutal reality of the human condition, its history, and, at the tectonic level of geopolitics, its current state. Author Martin based many of the plotlines of Game Of Thrones on actual historical events, with the War Of The Roses a frequent reference point. The brutal politicking, the lust for power, the manoeuvres required to survive, the ultimate difficulty human beings have in sharing land and resources in a spirit of mutual trust - all of these things echo throughout Game Of Thrones. Such were the mudheaps and rivers of blood that were slithered over and waded through in order to reach our precarious level of "civilisation", which today, and in times to come, may only be maintained by dirt, blood and metal. "The climb is everything", says the scheming Lord Littlefinger – be it his own climb to high office or the more desperate, literal climb to scale the great 700 foot wall that separates the northern wildlings from the rest of Westeros. Adding further to the sense of reality is the long winter currently being endured in Westeros, one which could possibly last many years, a resoundingly apt metaphor for our own, present condition of chronic recession, following the sunshine years of the 90s.

Then there are the characters themselves. Game Of Thrones is no morality tale. With the telling exception of the cowardly, psychopathic, unmitigatedly appalling young Joffrey, whose occupation of the throne is an indictment of the absurdity of monarchical rule, Game Of Thrones's characters are not so much heroes and villains, black and white, but painted in various shades of colour and grey, reflected in the overall look of the series. The Starks are worthy and honourable but also ploddingly dull and naïve. The Lannisters are devious, powerful but contain some of the series most charismatic and strangely likeable characters. Even Charles Dance's formidable Tywin commands a due respect, despite being the underwriter of so much of the show's misery. Daenerys, on a mission to liberate slaves as she sacks cities, represents an emancipated future but is herself chillingly imperious. Seemingly loathsome characters redeem themselves, or show themselves to be worthy of pity, while 'heroes' are often shown to be losers. "The good ended happily and the bad unhappily", Oscar Wilde once wrote. "That is fiction." That is not, however, the world of Game Of Thrones, to the frequent horror and exasperation of its fans, who curse Martin, but carry on watching.

Moreover, despite some invented argot in keeping with an invented world, the dialogue of Game Of Thrones is very much in a 21st century idiom. This isn't some daft sop to a mass audience, like Kevin Costner's transatlantic Nottingham accent in Robin Hood: Prince of Thieves. Rather, it reinforces the association of Game Of Thrones with the here and now. Best example of it is the series greatest character, Tyrion Lannister, played with immense stature by Peter Dinklage, an actor born with dwarfism. Memo to Ricky Gervais: This is how to present a short person on screen. Naturally, to reflect the ignorance of his times, there are frequent references to Tyrion's height, not least by his father, who considers him a "debauched stump". Dinklage is debauched, and a monied Lannister to boot, but he is also a pinnacle of decency in Game Of Thrones. One is barely conscious of his height as an issue. Rather, he strikes as a sort of Christopher Hitchens type cast at the centre of a medieval world, with a taste for the fleshpots but also informed by an urbane, solemnly knowing eloquence, regarding events with our own, liberal and informed sensibility.

There is magic in Game Of Thrones – white walkers, characters with the psychic ability to possess animals, sorcery, dragons and even, fleetingly and brilliantly CGI'd, a passing giant. The series is said ultimately to be about the return of magic in the world. As a rationalist who believes that the scientifically established physical and chemical order of things hasn't been tampered with since the beginning of time, this is a potential toughie. However, the magic elements are used only sparingly – the limitations of humanity remain very much the show's central attraction. This is a world in which there's no parallel equivalent of the arts, literature, scientific development or mass, bottom-of movements of humanity. It's possible to regard the magical elements as an equivalent of the forces undreamt of which will soon be at humanity's disposal, or have the potential to overwhelm them. Daenerys's dragons are young as yet, but as they grow, they will have a power in military conflict that's the equivalent of nuclear capability. She and they represent a future that is liberating but potentially devastating.

The word "game" in the show's title is as ironically, grimly apt as it is as in The Wire, with which GoT bears striking comparisons – not least in its refusal to conform to the convention of TV drama that all lead, heroic characters must be invulnerable to death. As in The Wire, no one is safe in Game Of Thrones and no one shall know (except those who have read the books) when and where the blade will fall. David Simon, creator of The Wire, always spoke of restoring to television the sprawlingly maximal and populous worlds presented in the 19th century novels of Dickens, Balzac et al. Game Of Thrones is very much in that new, sweeping tradition, one which is sweeping away the old fashioned modes of TV consumption, making the old fashioned model of celebrity-led Hollywood movies seem ridiculously constricted in their arc and scope by comparison with the great, ongoing longform TV dramas of our time. Game Of Thrones is set in a mythical past but in all kinds of ways it is representative of the very real present and future.