The cover art for this book should have been a photo of Cassandra Clare giving the middle finger to all of her fans. This book basically takes everything good about the original trilogy, throws it in the trash, and stoops down to the level of every other teen urban fantasy/paranormal romance on the market.
I really enjoyed the original Mortal Instruments trilogy. They weren't masterpieces, but they were fun. This isn't fun. This is Clare throwing together a completely unnecessary and plotless sequel to pad out her bank account, because she knows all of her devoted fans will buy it.
Employing incredibly lazy writing, Clare hardly bothers to write one sentence that isn't a cliche. There is no substance to be found here. The entire plot unravels into an endless drivel of trivial relationship drama. Her characters, who used to be interesting, have been eviscerated and are now one-sided stereotyped shadows of their original selves. When I read the original series in high school, I cared about these characters like they were personal friends. Now all I felt for them was mild irritation. After finally reaching the ending (the book culminates in a climax that goes on way too long and basically amounts to a bunch of characters being surprised to see each other) it even had me feeling like my enjoyment of the original series must have been poor judgement on my part, and I'd rather not revisit them to see what I would think of them now. City of Glass had already concluded this series satisfactorily, and I wish I had never read this continuation, which cuts every loose end that had been previously tied. I have no interest in continuing the series.