Tom Carson argues that the popularity of Game of Thrones has its roots in political cynicism:

Since noblesse oblige, let alone uppity input from the shaggy lower orders, are nonstarters here, nobody in sight even has to pretend to care about the public good.

This is seems true at first glance, but on closer reflection I don’t think it holds up. [Spoilers follow, so don't continue if you haven't read the books or watched the first season and would like to.]

While this description applies very well to the more despicable characters in the story (e.g., Cersei, Joffrey, etc.), it clearly doesn’t work for any of the maesters, the Night’s Watch, the Targaryen loyalists, or the Starks. Most of the characters have some political principles that they try to follow, but because these principles are unfamiliar or alien to our experience it is easy to overlook them or misunderstand them. The Lannisters go to war to defend the reputation of their house after Tyrion is taken captive. Robb Stark’s rebellion begins because of an insult done to the honor of House Stark when Ned is first imprisoned and then executed, and his bannermen have responded to his call for support as an expression of their fealty to him as their lord. Oath-keeping is the most important value in this system, and it creates the basis for broader political cooperation.

Supporters of a Targaryen restoration are royal legitimists who believe that the return of the rightful dynasty to the throne is essential for the good of the realm. They don’t call Robert the Usurper just to be insulting. They are appalled that there is a usurper on the throne. Even the ironmen have a sort of cultural-political tradition in the Old Way, which they are reviving in the absence of a strong central government. Both the Damphair and Melisandre are convinced that success and well-being are connected to endorsing the correct religion. Obviously, maesters trained to serve the realm in their capacity as advisers to their respective lords, and the Night’s Watch exists for the sole purpose of the realm’s collective defense. Except for people filling roles similar to those of the maesters and the Night’s Watch, we have none of this in our own domestic politics. Modern people are unlikely to find medieval or at least early modern political values all that appealing, but that doesn’t make stories that include them “rubbish.”