HBO put the "It's not TV. It's HBO." slogan into semi-retirement a couple of years ago. It had been around for nearly 13 years, and it was taken out of circulation (or occasionally shortened to just "It's HBO.") during a fallow creative period for the pay cable giant, when it was very hard to argue that the post-"Sopranos" version of HBO was really any different from any other channel.

But at HBO's early '00s creative peak, the slogan wasn't pretentious, but uncannily accurate. Shows like "The Sopranos," "The Wire" and "Deadwood" took stories and worlds that audiences knew to death and made them into something more - something grander in ambition, something richer in execution, something guaranteed to stick with you far longer than previous TV versions of that story had. "The Wire" was a cop show, and "Deadwood" a Western, but both were so much more.

The slogan's gone, but HBO has been mounting a comeback over the last year thanks to new blood like "Treme" and "Boardwalk Empire." Now comes "Game of Thrones" (it debuts Sunday night at 9), the expensive adaptation of George R.R. Martin's fantasy novel series "A Song of Ice and Fire," which is trying to do for the fantasy genre what the classic HBO dramas did for cops, cowboys and wiseguys.

And for the most part, it works - stunningly well.

Where I went into "The Wire" and "Deadwood" with a lot of built-in affection for their respective genres, I've never had much sentimental attachment for fantasy. I love the "Lord of the Rings" movies, but for the most part what gets adapted for movies and television is either laughably cheap-looking, more interested in fetishizing all the stuff about magic and kings and swords than in telling a good story, or both.

"Game of Thrones" is not that. Yes, it takes place in an alternate version of the Middle Ages - in an ancient collection of seven kingdoms where magic may have once existed, but which hasn't been seen in centuries - but it takes its world, its characters, and its stories seriously. There are kings and queens and knights, but they are always treated (by Martin in the books, and by producers David Benioff and Dan Weiss in the show) as people first, titles second.

The titles are important, but only in the sense that nearly everyone is jockeying for the big one: ruler of the seven kingdoms of Westeros. Martin loosely adapted the books' story from England's War of the Roses, and as we enter the world, Robert Baratheon (Mark Addy) has been king long enough to acquire a colorful and large rogues gallery of contenders and pretenders for the throne. His wife Cersei (Lena Headey) and her twin brother Jaime Lannister (Nikolaj Coster-Waldau) are conspiring behind his back, eager to see Cersei's son Joffrey (Jack Gleeson) take the crown as soon as possible. Viserys Targaryen (Harry Lloyd) and his sister Daenerys (Emilia Clarke), the children of the murdered previous king, live in exile and are trying to amass an army to cross the sea and reclaim their birthright. Each of the king's advisors is running his own individual hustle, and Robert himself is a gluttonous, spiteful drunk.

There are times when it seems the only man in Westeros actually suited to running the place is the one man who doesn't want the job: strong, fair, noble Eddard "Ned" Stark (Sean Bean), Robert's best friend, who controls the northernmost part of Westeros.

Those oddly-spelled names above represent only a small portion of the huge cast of characters in "Game of Thrones." Ned Stark alone has a wife, five legitimate kids, a bastard son, a "ward" and various close friends and advisors, almost all of them getting significant screen time. Yet even though the world is foreign and its people many, "Game of Thrones" isn't any more difficult to unlock than many of its top HBO predecessors.

Friends have been recommending Martin's books to me for a while, but I chose not to read them (for now, at least), wanting to see if the series could stand on its own and be both comprehensible and interesting to a newcomer. And it is. I probably struggled with identifying the members of the Barksdale crew in the early episodes of "The Wire" as much as I did trying to sort out the members of the House of Stark.

These characters all share complicated histories with one another - just as, say, Tony Soprano had pre-existing beefs with Feech La Manna or Richie Aprile - and there are occasions when the show starts to choke on all the exposition required to explain it all. The premiere episode is particularly talky, and Benioff and Weiss might have been better served if they'd chosen to occasionally show some of those past events, rather than just have people stand around and explain them.

But the characters are so richly-drawn, and so wonderfully-played, that the exposition ultimately isn't that great a stumbling block. I wanted to know more about these characters, and within an episode or so was eager for any bit of backstory that helped better clarify all the relationships.

The casting on this is really exceptional, from the well-known actors like Bean (who has the difficult task of making a man largely defined by his goodness not seem dull), Addy (fierce and commanding and completely unrecognizable from either "Still Standing" or "The Full Monty") and Peter Dinklage (having the time of his life as the Lannister twins' clever dwarf brother Tyrion) as well as relative unknowns like Clarke (who makes the virginal Daenerys' growing awareness of her power, sexual and otherwise, into one of the series' strongest ongoing arcs) and Maisie Williams (a delight as Ned's tomboy daughter Arya).

It's a mark of how well-crafted the show is that I didn't find my attention wandering during scenes involving the types of characters who usually put me to sleep on other series, fantasy or otherwise. I usually find bratty, willfully ignorant kids a chore to watch (take Elizabeth Mitchell's "V" son - please), but I found myself understanding (if not particularly liking) Ned's snotty, status-conscious daughter Sansa (Sophie Turner). Ditto the Lannister twins themselves, as I rarely have any interest in the catty scheming types; Headey, Coster-Waldau and the writers make them into three-dimensional, interesting figures.

And even as the series is demonstrating its ample commitment to story and character, it still offers all the nifty visual bells and whistles that you find in abundance in more shallow fantasy stories.

The pilot episode (mostly directed by HBO veteran Timothy Van Patten after an earlier version by Tom McCarthy was largely scrapped) is a feast for the eyes. The different corners of the world all have their own memorable looks: the arctic chill of the giant wall separating Westeros from its primitive, deadly neighbors to the far north; the lazy tropical ambience of the nation's capital; and the mix of seaside beauty and Great Plains simplicity of Daenerys' new homeland. A later episode brings us to the Eyrie, a mountain stronghold that has one of the most diabolically simple fictional prisons I've ever seen.  

There's also abundant violence (it's like a masterclass in beheading techniques) and sex (particularly in, but far from limited to, the scenes with Daenerys and her primitive new husband, played by Jason Momoa). It's an adult series in every possible way. But where a comparable show like Starz's new "Camelot" might throw in the nudity just as a lure to get people to watch, the sex scenes in "Game of Thrones" almost always have major narrative value, whether they're establishing a foreign culture or telling us more about a character who plays things close to the vest outside the bedroom.

It's far too early to say whether "Game of Thrones" will ultimately belong in the HBO pantheon, but it has so many things in common with those shows.

Like the best of the HBO dramas, "Game of Thrones" has more on its mind than telling a good story within its chosen genre. In its alternate take on English history, it has a lot to say about the appeal and danger of power, about the never-ending tensions between economic and military forces, and the similarly eternal clash between idealism (Ned's vision of rule) and pragmatism (Robert's).

And like "The Sopranos" and "The Wire," it has one hell of an opening title sequence: a soaring tour through a map of Westeros and its different corners, with each kingdom or garrison rising up from the ground like clockwork toys. Not only does it help orient newcomers like me to this sprawling place, but it says so much about how this world is one incredible playset, first for Martin, and now for Benioff, Weiss and company. It was a place for Martin's imagination to run wild on the page, and now for everyone else (including Martin himself, who wrote one of the later episodes) to bring that imagination to three-dimensional life.

There's so much going on in this series - so many people and places and rules to learn - that I feared I would be completely lost without the books as a roadmap. But as with the cream of the HBO crop, "Game of Thrones" deposits me in a world I never expected to visit and doesn't leave me feeling stranded and adrift, but eager to immerse myself in the local culture.

Alan Sepinwall may be reached at sepinwall@hitfix.com

***

NOTE: Because I haven't read the books, and because I imagine (unless the show is an utter ratings disaster only appealing to the die-hard GRRM fans) more viewers than not will be in my boat, we're going to take the same approach to discussing this show as we have to "The Walking Dead" and many other adaptations. I don't inherently object to discussion of the books, but I also don't want detailed (or really any) plot discussion. (There are plenty of fansites where you can do that at length.) In my weekly episode reviews, we're not going to discuss anything from the books that takes place after the events depicted in that particular episode (and while I know Benioff and Weiss have moved a few pieces around, we're still going to stick to the general timeline). So you can talk about, say, the direwolf cubs after they appear in the pilot, but don't say anything about what they're going to wind up doing in later episodes until we get to those episodes. Got it?