Sean Bean portrays Lord Eddard "Ned" Stark in a scene from the HBO series "Game of Thrones," premiering Sunday. (Nick Briggs/AP)

The grand but unwieldy new HBO series “Game of Thrones” is based on a successful series of medieval fantasy novels (more than 7 million copies sold since 1996) by George R.R. Martin, whose fans are so eager for another installment — as an article in the New Yorker recently described — they’ve built Web sites devoted to browbeating Martin about the many years it has taken for him to write the next book.

In this, the age of post-geekdom, fans such as these are now accustomed to getting what they want in our culture; they are even spoiled rotten, up to a point. They all but demand big- or small-screen adaptations of their favorite novels and comic books, their swoony vampire sagas and magical-mystical whatnot. Producers, sensing a built-in and fierce loyalty, aim to cash in. Woe betide ye wretched critics who deign to disparage the beloved source material. And God help ye network executives who try to cancel one of these things after a lackluster season. Ye shall be punished.

But the fact remains that franchises such as “Game of Thrones” (which begins Sunday night) tend to repel those whose tastes in TV and movies are broad and omnivorous; we find ourselves intimidated by the required emotional investment. We don’t want to be hard-core fans of anything. We don’t go to conventions or write e-mails to our favorite authors. We want diversion for an hour or so, then we’ve got other stuff to do. Yon laundry and such.

It used to be that the people whose worlds revolved around fantasy and sci-fi lived in a fringe media territory, sometimes proudly so. Now it’s the other way around. You’ve never heard of “Game of Thrones?” You’re not feeling so hot about another complicated series involving swords, wenches, dwarfs and kingdoms? Well, that is your fault, then, for being so un-nerdy.

All of which is to say that even for the most open minds, “Game of Thrones” can be a big stein of groggy slog.

On the plus side, the first six episodes are impressively free of sorcery and special effects, and instead rely on the stuff of any deeply dark HBO epic: corruption, deceit, illicit sex (incest in this case), unflinchingly gory violence, and a willingness to kill off a prominent character or two in the service of plot. When “Game of Thrones” breaks out in sword fights, it does so with exceptional style and vigor.

On the down side, and also like a deeply dark HBO epic, it has a lot of characters and story lines to keep track of.

It takes place in a world called Westeros, a Tolkien-esque Middle Earth of long ago, where summer can last for decades, but the winter, when it comes, can last even longer and bring with it a feared race of monsters called the White Walkers.

Way up north, in the realm of Winterfell, Lord Stark (he goes by Ned) and his large family are visited by Ned’s old war chum, King Robert, who has made a month-long journey to ask his friend to become his second-in-command. To the chagrin of his wife, Lady Catelyn, Ned accepts the job.

I could spend the rest of my space here (and a year’s supply of “meanwhiles”) just trying to give you a sense of how many story lines are launched in only the first episode. Like this: Meanwhile, across an ocean, a tribe of beastly warriors agitate to invade Westeros and reclaim the throne on behalf the dragon people, who were overthrown a generation ago . . .

In Westeros, King Robert is married to Queen Cersei, one of the wealthy, always-blond Lannister family — a political marriage rife with disdain and opportunism. The queen has two brothers, one of which provides the only real standout performance of “Game of Thrones”— Peter Dinklage as Tyrion Lannister, a suave and hilarious dwarf.

There had to be a dwarf, right? It’s our good luck that it is Dinklage, who is saddled like everyone else with pretentious-sounding medieval dialogue, but manages to speak it as though it’s a newly discovered work of Shakespeare.

“Game of Thrones” is deadly serious about its thees and thous — a fantasy trope that pop culture has been mocking since Dungeons & Dragons emerged from the basement rec-room to invent Google. Kidding aside, it is possible to admire “Game of Thrones” for its sincerity and clarity of purpose — its utter devotion to form and detail — while the rest of your TV brain struggles to keep pace with what happens. Some cohesive magic does eventually take hold, and it gives the series a “Rome”-like layering and momentum.

The eternal question is, are you up for the journey?

It’s about becoming (or not becoming) the kind of viewer who can sign on to such a daunting amount of Dark Ages hoo-hah. That’s a personal genre choice, and one I’m pretty sure I made as far back as 1981, when a friend’s sleepover in middle school turned into my first and final encounter with Dungeons & Dragons. I was so quickly bored by the whole idea that I wound up in the kitchen, helping my friend’s mother make Rice Krispy treats. My fate — and my kingdom’s — were thus forever sealed.