The book is the first in a series. It is long, and complex. Martin switches perspective every chapter, there are lots of characters, and it is highly detailed. SO, it takes a little while to get into it. The characters are nicely fleshed-out, though, and you'll begin to care about them pretty quickly. The book is low fantasy, set in a kind of medieval world made up of 7 united kingdoms, as well as a few others. The king who is currently on the throne took it by force, overthrowing the mad king, who had inherited the throne, and killing or banishing his offspring. The new king is pretty well-loved, but not by his wife, and if something should happen to him, what will happen to the kingdom?
A few things to be aware of: the book contains sex, violence, and incest. Martin also has no problem killing off characters--even main characters, so don't get too attached. Despite being so long, the book really is compelling and a page-turner. You'll want to have the 2nd one waiting in the wings for when you finish.