Across America, fans of the epic fantasy drama Game of Thrones will tune in on Sunday night to find out how the brutal, breathtaking fourth season ends. Will the sharp-tongued fan favourite Tyrion Lannister, unfairly accused of the murder of his evil nephew, be executed? Will The Wall fall? What will happen to the youthful killer-in-training Arya Stark?

British viewers will have to wait until Monday to learn the answers, but the Game of Thrones effect reaches considerably further than the 66-minute episode that the show's writers, David Benioff and DB Weiss, have claimed is "our best finale yet".

Last week HBO announced that the adaptation of George RR Martin's best-selling books was now its biggest hit, surpassing The Sopranos in viewing figures. It dominates the cultural conversation, referenced in everything from sitcoms to political debate. Now it is remaking television in its image.

The success of Game of Thrones has led to a proliferation of big-budget epic dramas. Some, such as Vikings – the first two seasons of which are available on Amazon Prime Instant Video – are straightforward historical stories but set in a similarly brutal world. Others, such as the adaptation of Diana Gabaldon's Outlander saga that US cable channel Starz is currently filming in Scotland, are fantasy tales that would never have been made but for the HBO show's success.

Indeed Outlander's executive producer, Ron Moore, recently admitted as much, telling Entertainment Weekly that Game of Thrones "definitely opened the door and showed that fantasy and genre material has a strong audience on premium cable".

Like Game of Thrones, the Outlander novels – an addictive mixture of time travel, historical epic and romance – have a passionate following. The eighth book in the series, Written in My Own Heart's Blood, was released last week and expectations are high that the TV adaptation can tap into Game of Thrones' success to become a worldwide phenomenon. A UK deal to air the drama is reportedly close to being finalised, while it has already been sold to Australia, Canada and Russia. As Moore explained to Entertainment Weekly: "Game of Thrones has shown you can take an existing readership and turn it into an audience and then broaden that audience."

Television's newest power, Netflix, is equally bullish about its epic drama Marco Polo, which will begin filming in Kazakhstan, Italy and at Pinewood's Iksandar Malaysia Studios this August. The 10-part mini-series stars the Italian actor Lorenzo Richelmy as the explorer and is executive-produced by Harvey Weinstein in his first foray into TV drama. Early descriptions have promised a very Game of Thrones-sounding mix of "political skulduggery, spectacular battles and sexual intrigue".

Yet Benioff and Weiss's mix of high drama and low morals is surprisingly tricky to emulate. The White Queen, cancelled by the BBC after one season (although Starz may yet make a sequel), was a disastrous combination of schlocky dialogue and heaving breasts. The swashbuckling historical fantasy Da Vinci's Demons is thought to be fun, but far too kitsch to take seriously; while of two recent pirate dramas, Black Sails, currently available on Amazon Prime, manages the rare feat of making copious amounts of guts and gore seem tedious, and Crossbones is more pantomime than prestige viewing, although worth a look for John Malkovich's bizarre accent.

Nor is everyone convinced that the success of Game of Thrones has opened the floodgates for a host of fantasy dramas. "It's hard to find a fantasy epic that has a strong fan base already and that is as intricate as this one and then get to a point where the production values make the suspension of disbelief plausible," says Gawker's Michelle Dean. "I mean, even with Game of Thrones I'm often like, 'Goddamn, why can't they get eyebrow dye into the budget?"

Even a strong fan base is not always a guarantee of success: last week HBO's president, Michael Lombardo, admitted to New York magazine that it had pulled the plug on an adaptation of Neil Gaiman's fantasy American Gods because "even though we love the book, we love the idea … we just couldn't get it right … we tried three different writers, [but] some things just don't happen".

Meanwhile, those who enjoy the political machinations of King's Landing but would prefer it without ice zombies and dragons can sit tight and wait for next year's biggest treat: Peter Kosminsky's take on Hilary Mantel's Booker prize-winning Wolf Hall, starring Mark Rylance and Damian Lewis. It might not be fantasy, but the schemers and dreamers of Henry VIII's court would make even Tyrion Lannister think twice.