First off, I want to say that I was really eager to read this book. I will admit that I wasn't greatly impressed with Ms. Clare's earlier books (this book is the fourth installment in what was originally a trilogy, more on that later), but the smart-ass one liners and "more action, less gratuitous sentiments of love" plot was enough to keep me mildly entertained. It was a very very decent guilty pleasure. (I have relatively few, because I tend to get too annoyed at protagonists after awhile)
I was hesitant to re-start what I thought had been a finished trilogy, because it, with a few exceptions, rarely ends well. Many times it feels like the author has struck gold with this book/series alone, and the author is reluctant to branch out, so is milking X cash cow for as long as possible.
<If you have not read City of Glass, be warned, the following contain spoilers>
The City of Fallen Angels, fourth book in the series Mortal Instruments, starts a few months after its predecessor, City of Glass, ends. Simon is still a vampire, Clary is a Shadowhunter in training, and Jace is still brooding over whether he deserves happiness or not. Throughout a long line of angst and bad dreams and seemingly impending power plays, the reader gradually learns that Jace's evil foster brother is being planned for a resurrection by a powerful demoness, using Clary's request to resurrect Jace in City of Glass as a loophole. (Tsk, Clary. One request and the fabric of reality suddenly shifts.) Oh, and Simon leaves home, but he (and the reader) stop caring after a few minutes. Minor character Maia's old boyfriend shows up, repentant and part of some secret society. An old vampire named Camille comes back to reclaim New York, but she may or may not be evil, and Alex is annoyed at Magnus once he discovered Magnus dated hundreds of people before him. All this takes a backseat to Jace's angst and Clary's confusion.
I'm going to come out and say it: This book is trash. Through and through. I can't really think of a single redeeming factor. Ms. Clare had a pretty decent series wrapped up, and it should have stayed that way.
Jace's angst, once endearing to one degree or another (or, if not, at least redeemed by his rapier wit) has now become not only a plot device, but purely irritating. He doesn't believe he deserves happiness, and also he has bad dreams, so clearly, the solution is to drive his one source of happiness out of his life. Clary, on the other hand, fails to show any sort of personality traits except determination to keep Jace and also to find out what is bothering him. Admirable traits, to be sure, but she seems to be neglecting everything else. We can't blame her - the whole plot turns out to be hinging on Jace's angst.
Simon's turmoil (apparently the Mark of Cain should have DIRE consequences) happens because he decided to 'come out' as a vampire to his mother, who doesn't take it too well. He hypnotizes her and runs away, moving in with Maia's ex-boyfriend, who apparently was abusive but it's okay because he was just a young werewolf and couldn't control himself yet. Maia doesn't forgive him (props for that) but the rest quickly warm to his presence, even angsty and suspicious Jace.
This book has a lot of loose ends. I suppose we can expect that, seeing as Ms. Clare plans to have two more books before this series wraps up for good - I personally, will make sure to read many reviews of the said books before I pick any of them up. This one was a disappointing waste of time.