Okay overall. (this review contains spoilers)
Let me start off by saying that this was not a bad book. The plot was generally interesting (although I felt that one could chop off several filler paragraphs without materially affecting the story) and the writing was clean enough and moved quickly despite the aforementioned fillers. The reveals of the backstories also seemed quite forced - but they were thorough and tolerable enough. The dialogue could border on painful sometimes, and the book-and-poetry quoting could get annoying.
However, it annoyed me that several characters were very similar to characters from TMI - Tessa is like a snarkier, more 'ladylike' version of Clary - however as heroines go, she was consistent enough, if a little boring. Both Jessamine and Isabelle are beautiful, competent, slightly mean Shadowhunters on opposite sides of feminism. But what annoyed me the most was that Will and Jace could essentially be the same character - only Will just happens to be much meaner and much ruder, and the fact that he was nice one moment and sarcastic the next and then sad and haunted was incredibly irritating. Troubled But Cute
or deep dark secret or whatever, it just added to the overall annoyance.
Their relationship also had lots of similarities with Jace and Clary - naive-but-powerful-fish-out-of-water-girl with hot-competent-emo-Shadowhunter guy. It just got kind of old, and I don't see how Will being insanely emo (bipolar or not, it just felt that way) made things any better. It felt rather forced.
I liked Jem, who seemed to have a tangible character at least - despite it being the old kind, handsome but tragically ill Love Interest
trope, and his friendship with the brooding Will was a little endearing. However, I severely disliked Nate and the forced, unreal way with which he seemed to switch sides, and his relationship with his sister was not nicely portrayed. The servants and the villains were also pretty cool (special mention to Sophie), and the villains did have a point with the Fantastic Racism
which was, sadly, never really fully explored by the book like it was in TMI. Another thing was that the twists were getting very predictable, and there were way
too many problems left unexplained - such as the angel necklace.
Overall, the book is lacking in some aspects - but since it's only the first book, there is plenty of time for improvement.