A story lives or dies by its characters. It's trivial to write about dastardly villains and brave heroes; not so easy to give the characters depth and make them into real people that we actually care about.
In A Game of Thrones, George R.R. Martin accomplishes this difficult task and makes it look easy. Dealing with a veritable army of leading characters from several noble families, Martin uses the simple but entirely appropriate technique of devoting each chapter to a single character's point of view.
Most of the vignettes in Game feature the Stark family, a clan with their home at Winterfell in the northland. The Stark motto is "Winter is Coming", and as the story opens, a summer many years in duration is quickly fading towards a time of cold and darkness. North of Winterfell lies the Wall, a massive ice structure that protects the kingdom from attack, but inauspicious signs suggest that the kingdom is not safe.
To the south, other battles rage: Intrigues among noble houses, rival claims for the throne of the realm, alliances and betrayals, cunning and idiocy.
Game is illuminated by the theme of being true to oneself, of trusting one's instincts and acting upon them. Some characters succeed in doing this; others do not. Internal conflict and difficult decisions make this a mesmerizing story, with startling reversals of fortune coming out of seemingly isolated events.