A Clash of Kings (ACOK) picks up right where it's predecessor Game of Thrones left off. The red comet seems to appear as a sky as a result of the birth of Daenerys' three dragons at the end of the previous book. This ominous sign in the sky is commented on by all of the point of view (POV) characters throughout the first third of the book, and this sign cannot help but drive the subsequent actions by the characters.
The prologue is certainly longer in ACOK than Game of Thrones, but a lot of ground is covered. The reader sees Stannis (albeit through the eyes of Maester Cressen) for the first time in this series, and he is clearly a curmudgeon that is seeking his due. Stannis is pushing all his chips to the table by aligning himself with Melisandre, the red priestess. The elderly Cressen tries to prevent Stannis from recklessly attacking the mainland, but here (and throughout ACOK) the faint of heart are pushed out of the way. The long prologue is foreboding and tense throughout, and really sets the stage for what follows in the main narrative.
The Stark family has been scattered throughout Westeros, and the narrative seems to be pulling the Stark POV characters even further apart from each other-Jon going deeper beyond the Wall, Arya and Catelyn like two ships passing in the night without ever spotting each other, Sansa remains trapped in King's Landing while Bran tries to rule in Winterfell. None of these five Starks are in control of their travels, while the one Stark who does have some control (Robb) is only mentioned through other characters. Honestly, I'm not sure why Martin kept Robb off-screen, especially where he is involved in some battles during ACOK.
Davos' Seaworth's chapters are highly interesting, especially as it tries to explain why a former smuggler is so loyal to his lord that aspires to the throne. Theon's initial chapter is quite funny, and sets up how he wants to prove himself throughout the remainder of the book.
Initially, I did not find Daenerys' chapters as interesting, although her foray into the House of the Undying was quite well done. I really enjoy how Martin peels off the onion layers of the Targaryen past through Daenerys' chapters.
However, Tyrion is truly the one that dominates a lot of the action in ACOK. Martin has created a fantastic character in Tyrion that resonates well beyond the scope of this series. Tyrion makes himself a force to be reckoned with all characters (including his sister the regent) despite his small stature.
About halfway through the book is building to a climactic battle, only for that opportunity to be snuffed out. However, this only serves to create more tension leading up to the climactic battle of King's Landing. The battle was quite riveting, especially as told through multiple viewpoints off the battlefield and on it. Martin truly shines when writing this battle, and it's easy to see why he wanted to use books instead of television as his writing forum.
The final chapter is a shattering aftermath of battle told through Bran's eyes. I've never been a big fan of the Bran chapters, but this one resounds with the reader.
This is a strong sequel to Game of Thrones that creates even more tension for Storm of Swords. My only criticism is that some of Robb's actions should have been seen through a viewpoint character, but the bulk of the action was taking place in other locales. Martin delivers another long yet tight narrative in the second book sating the reader for the moment....yet making the reader want to dive immediately into Storm of Swords.