Before I say anything else, let me be quite clear. Like all of her other work, I loved this book. The action is perfectly presented, the conflicts are compelling and there is no such thing as a flat character. 
 I always adore this world. Everything about it is perfectly flushed out. More than any other fantasy world, I want to live in this one. The brain that hatched it is truly brilliant. And this book expands on many aspects that the other three did not. But, by the very nature of it being a prequel, there are things the readers know that the characters do not. I love dramatic irony. 
 The setting is completely realistic. Being a European history geek, I love the "steampunk" movement and all of its aesthetics. It is an amazing morph of history, changing it into something even more awesome than actual Victorian England. Clare describes it so vividly, the sights, smells, tastes, just the feeling of Victorian London is perfectly presented. And, by her own admission, she changed things about the city. But only for the better. 
 The story is very well-constructed. Like many YA fantasy books, I had solved the mystery long before the characters, and there was no point in this book that made me gasp (unlike City of Ashes!), but it was still a great read. Unlike many authors, Clare meshes character development and motivation perfectly with the construction of the plot itself. They drive one another, instead of existing separately. Like her other works, the ending was not a storybook happy ending as seems to be the inclination of everyone in the genre right now, but was instead something believable (and altogether too much of a cliffhanger!). 
 As usual, Clare also has a perfect sense of timing and wit. I laughed out loud on multiple occasions, even in public places, and then I cried (just a little) at the end...in a depressed rage. I'll leave it at that. She does like to tug on your heartstrings. Just read it. 
 Will is hot, but nevermind him. Jem is so much more amazing. Tessa is a moron. This was the "painful" part. I rooted for Jace in the other story because "nice guy" Simon was kind of pathetic in comparison, but there is nothing pathetic about Jem. The man has a cane with a sword in it. Will can go jump off a cliff. 
 I absolutely love this book, and I look forward to more installments in this series (not to mention City of Fallen Angels, which comes out in April 2011 and Clockwork Prince next fall!).