I think it's safe to say that anyone who is reading or has read A Clash of Kings thought well enough of the epic George R.R. Martin began in A Game of Thrones to continue the saga. I can't very well picture someone trudging through book one, hating it, and saying, "Well, that was complete rubbish, why don't I try out another seven hundred pages of the same!" A Clash of Kings is the book for those that devoured the relationships, battles, power struggles, alliances, and betrayals that began A Song of Ice and Fire and were more than eager to explore the second verse.
Yet, A Clash of Kings is also likely to gain a new audience very soon. HBO's series Game of Thrones follows the saga told in book one, and I predict that if the season ends with the same cliffhangers as the book, many watchers could be running to their local bookstore or library hungry for a continuation of the plot. Some die hard fans may start reading at the beginning, but I expect that several fans will jump right from the show into book two. (Quick note: I'm not currently watching the series but I have high hopes for it and may even plan a weekend DVD binge when it's released on disc.)
The glorious thing about this arrangement is that Clash of Kings is equally as good as Game of Thrones. HBO will serve to draw new readers to the epic series and even if they jump in at Clash, there is plenty to hook them and hold them through the next few tomes. The story begins where Game left off with multiple individuals claiming crowns of their own. And Martin's pattern of killing off those bearing titles of royalty continues - though I'll not say which or how many of the rulers survive through this volume. There are favorite players that continue to shine, and new narrators whose perspectives cast new insight on leading characters. Some are intriguing enough that the reader wants to hear more of their story and some are so vile that the reader hates to be inside their heads. (Yes, Theon, I mean you!)
In short, A Clash of Kings is a worthy follow-up to A Game of Thrones. In some ways, it could be seen as just more of the same, but that write-off minimizes the expansion and growth that Martin continues to pour into the series. The unpredictable quality of the plot ensures that this is not a series for those looking to find a "Happily Ever After" at the end of the tale. Rather, it is a series for those who don't want stories to end - for if A Clash of Kings promises anything it is that - even after 1000+ pages - A Song of Ice and Fire has only just begun!