Game of Thrones, Sky Atlantic, Monday<br/>The Walking Dead, Channel 5, Sunday<br/>Twenty Twelve, BBC4, Monday

Apparently a producer of Game of Thrones now regrets describing the TV adaptation of George R R Martin's fantasy novel as "The Sopranos in Middle Earth".

Whatever throat-clearing followed that pronouncement, it's nonetheless revealing of the series' ambition: an attempt to bring some dramatic badda-bing to a genre that, Peter Jackson's Lord of the Rings films apart, has yet to cast a spell over mainstream audiences. Of course, what equates to HBO's great New Jersey crime-family saga in the fictional, muddy realm of Westeros is another question.

There's the graphic violence, I suppose. Guts are spilled and heads lopped off, at some trouble to the art department. But it feels justified: in the opening – and best – sequence in the first episode, the discovery of a massacre concludes with yet more blood-letting in a manner that not only tees up the narrative, but also indicates that life in Westeros is nasty, brutish and likely to be shortened by a long sword. There's the sex, too, which included incest and an orgy with a dwarf. All shown no doubt, to illustrate that intercourse is just another crude form of currency in this seemingly medieval society. A shame, then, that the cameras seemed to linger clammily over all the young female flesh on display.

You'll have noticed that I haven't attempted to unpick the plot – something about the four great houses of Westeros struggling for the "iron throne". From what I could gather, King Robert (Mark Addy) requires the help of his old friend Eddard (Sean Bean) to defend himself from the designs of the brattish pretender Prince Viserys (Harry Lloyd) and his accomplices, the Dothraki, who ride as fearlessly as they apply their mascara.

But neither do the screenwriters have much appetite for these dynastic wrangles. How else to explain the sunset, al-fresco, cliff-top marriage of Viserys' sister to a Dothraki potentate which seemed to working from a mood board you might call Channel 5 soft-porn, c1998? The scenes between Robert and Eddard were an improvement, if only because no one can do moody in furs quite like Sean Bean. But for the most part these passages of exposition ground by without any of the wit or vim that, say, that HBO-BBC co-production Rome brought to another empire in turmoil. At least Peter Dinklage as the mischievous "imp" of the Lannister clan has the decency to look bored.

More promising were the passages which suggested that there was some sorcery to go with all the sword'n' sex. The first quarter of an hour brooded nicely over the stirrings of sinister supernatural forces to the north of a great wall that Sean Bean's people have manned for thousands of years. But The Sopranos in Middle Earth? Fuhgeddaboudit.

Sean Bean wasn't the only Brit wielding an axe in a strange land this week. In The Walking Dead, Andrew Lincoln brought down a few zombies with one, while trying to rescue a group of people trapped in central Atlanta. Lincoln plays an American lawman, Rick, who has awoken from a coma to find that the country is plagued by flesh-eating "walkers".

I missed the opening episode, but soon learned in this, the second, that Rick is struggling to find his wife and son. The makers of this solid-genre entertainment seem to know where they're going, though: a splatter-fest with the occasional satirical touch. So, Rick and his fellow refugees find themselves besieged in a department store, the undead pressing against the locked doors in a way that anyone who has worked retail in the January sales will find uncannily familiar. Later, to pass themselves off as zombies and secure their escape, Rick smothers himself in human viscera so that the zombies won't pick up his delicious scent. But, would you credit it, a cloudburst ruins his new look.

To which Ian, the chronically embattled head of deliverance for the London Olympic Games, might say, "That's all good." After a shaky start, Twenty Twelve developed over its six episodes into a thoroughbred example of that old comedy nag, the mockumentary. Last week's closing episode was case in point – correctly confident in a commission for a second series, it tied up none of its story lines with "734 days to go" and instead delivered a masterclass in comedy, both technical- and character-driven.

Ian's nemesis here was Tony, an embittered old film-maker determined to scupper the equestrian events planned for Greenwich Park. Tony was beautifully played by Tim McInnerny, but the pleasure, as ever, was the sleight of hand on display: the razor-sharp editing, the blink-and-you'll-miss-it sight gags (Tony thumbing through a script entitled "Nail Me To My Car"), the verbose narration. Let's hope Lord Coe can produce something half as entertaining next summer.