For my money, the best part of HBO’s hit series “Game of Thrones,” is still the opening credits. Under a giant gyroscopic sun, a map of the seemingly generic fantasy world “Westeros” comes to life with baroque, unfolding CGI toysets of the show’s major locations. As the show enters its second season, new places get added almost every week to the Transformers-meets-Lincoln-Logs tour.

It’s an apt metaphor for the show’s appeal: like its source, the high-pulp fantasy book series “A Song Of Ice And Fire,” the show takes creaky clichés that most respectable people shun and drops them into a brutally complex political arena.

Halfway through the second season, the show isn’t something you can jump into (or even summarize coherently). The accessible political intrigue of the first season’s blondes-vs.-brunettes slow burn has evolved into full-scale continental war; this season has given us three new kings, kingdoms, and casts of characters trying to seize the Iron Throne, the chair made of swords that you saw on all the billboards last year. Hardened politicians and royal families treat war like a board game while peasants and soldiers feel the devastating repercussions. If that’s not enough, there are subplots about royal bastards, fugitive princesses, zombies, dragons, and warlocks, all living in poverty on the extreme margins of society.

Although it’s one of the best things on the air, the appeal of “Game of Thrones” contains a degree of morbid fascination: how could such a downer show with so much dorky genre stuff have such ridiculous ambitions, such a big budget, and such good reviews?

The answer is a solid foundational goal of twisting the conventions of science fiction and fantasy on their heads. Adapted pretty directly from the books, every scene contains some reversal of the stiff gloss and simplistic morality of whatever else is in the “Science Fiction/Fantasy” section at Barnes & Noble. Most main characters are fighting for their lives hundreds of miles away from where you expected them to be, the dragons are tiny, the enchanted weapons and animal companions are torn from their owners, and to top it all off, there are a million prophecies of doom—but everyone is too focused on other things to care. While the show’s darkness is relentless—even overbearing—it’s rarely tacky; it stems from an honest desire to make something fresh out of stale parts. The dismissive cynicism with which the show treats its cast never reaches the audience.

As much as playing with viewers’ expectations is part of the show’s central appeal sometimes those expectations get the better of it. People come for fidelity to the books’ cynical web of plotting, for HBO’s brand of “quality TV” (which includes a lot of violence and sex scenes), and for a grittier Lord of the Rings, so the juggling act sometimes falls apart. You need only compare the creaky pacing of Episode Two to the frenzied soap opera of Episode Four to see how tonally unpredictable it is. While its only television rival for sheer density is “The Wire,” it replaces that show’s rich Baltimore idioms with a corny tin ear for dialogue (one of the showrunners wrote “Troy”). With the exception of Peter Dinklage’s Tyrion as well as spots of half-assed gallows humor, the show’s characters are exhaustingly cold despite a cast of great actors. Some scenes the show has added, such as a recent one involving prostitutes and a crossbow, are just too much. Revisionist as “Game of Thrones” may be, we’re still stuck in the blunt, taking-yourself-too-seriously attitude of the Syfy Channel, and in its weaker moments, only the mental exercise keeps us engaged.

Don’t let that deter you if you like this kind of show; it’s shaping up to be the best DVD boxset since whatever HBO’s last addictive epic was. Scenes can slog, and it’s hard to muster up the self-congratulation that comes with committing to a good, deep series when the sex scenes can be so embarrassing, but the immaculately unpredictable storytelling is so impressive that any flaws just pull the show down from great to really, really good TV. It’s already taken risks in making this season so much grimmer and faster than the first, so once it finally gets a sure footing, I’m guessing it’ll be the best thing on the air.