In this story, Jace and Clary are back to their old antics as they continue their struggle against the infamous crusader, Valentine. Joined by the old gang, Jace and Clary travel from place to place, argue, travel, argue... and that about sums up the story. I'm not saying that City of Ashes was a bad book. In fact, I loved it. I think the premise is intractably constructed and Clare writes with artistic brilliancy. However, the story is really driven (haha) by travel and arguing.
There was also plenty of twists and turns as I have come to expect from Cassandra Clare. The characters are well-developed and believable - though I do question the authenticity of the Inquisitor's motives. The Jace/Clary relationship is slightly disturbing and I felt that it was a bit of a distraction from the overall flow of the story. Other than those small irritants, the story flowed pretty much flawlessly.
In terms of originality, Clare nails it. She does borrow a few of the more overused mythological creatures in popular culture, but it doesn't affect the structure of the story. If you loved book one, then you'll probably love book two. I'll be reading book three, but not any time soon. City of Ashes left me feeling somewhat underwhelmed. That's just of my own opinion.