Overall, this book was highly entertaining and action-packed, which I crave in fantasy novels. The dialogues and characters had high doses of reality and humor, so much so that the characters themselves became real to me (while reading I was watching Clary and Jace argue in my head).
Let me also say that this book throws you for an absolute loop. While some may have guessed the plot twists, I was completely surprised and am still getting over the shock. The whole romance-turned-siblingship between Clary and Jace was disorienting AND, I felt, unnecessary. You spend the whole book fighting inwardly between the two potential romances with Simon or Jace, only to have one option completely thrown out of the window--when authors do something like this, it's usually emotionally tied, like the boy cheating or being secretly evil. But turning Jace into her brother made all the feelings you, as a reader, had for the couple completely creepy. It seemed almost like a punishment: let's spend all this time building up Jace and showing that he's more than a pompous prick, only to find out that our feelings are completely worthless. Ouch.
Quite honestly, those plot twists make it difficult for me to want to continue with the series. All the relationships' mystery was completely taken away, and without mystery, it's hard to keep reading on. To potential readers, I urge you to read with an open mind and be wary, because Cassandra Clare will take you on an emotional roller coaster.