2.5 stars. Basically a spoiler-free review.
This is probably going to be a very short review because I have a very limited amount of feelings towards this book that more or less start and end at No.
Don't get me wrong, I didn't hate the book overall. I didn't even dislike it. The main issue that I had with the book was the Clary/Jace desperate pining that made me want to claw my eyeballs out. It seemed that every time something actually started to happen with the plot, the entire book had to pause so that either Clary or Jace could try to bring up their feelings for each other, only for the other to counteract them and say that it's wrong. The worst part is that that's exactly how it happened Every. Single. Time.
Now here's the thing, I don't have any feelings towards Clary being into Jace or vice-versa. They can go make out for hours if they want to, that's up to them, but what I do have a problem with is the overrunning theme that it's forbidden and wrong because they're siblings. Either let them be together or make them stop acting like star-crossed lovers, or just stop talking about it so that we can actually focus on the plot of the novel! That's actually something I care about because the rest of the characters in this series are actually kind of interesting!
First off, the plot is pretty decent. The first half of of the book feels like it's constantly summarising the first book, which I found annoying, and by the 50% mark I felt like nothing really had happened other than Maryse and the Inquisitor were both terrible people and Clary was once again whining about her undying love for Jace despite knowing him all of a few weeks. The only thing that made this book alright for me was the whole spiel with Simon being turned into a vampire, Alec's declaration about seeing Magnus to his parents, and, well, Magnus Bane as a whole because he's the fabulous bisexual warlock that I constantly aspire to be.
Overall, the novel was okay. It's not something I'd ever reread, and the epilogue was terrible and really didn't need to be there at all, but it's okay. Two books down, four to go. Hopefully they start getting better at some point.