I like the books really. Just as the author I like very much what I know of their more than successful fanfiction. Cassandra Clare has an unbeatable sense of humor and knows how to build tension, which she also brings good in these books.
What about the show something bothers me - particularly in the last volume - are the secrets is to work towards the "slow". The author interspersed throughout the book every now and then a Notes, and then dissolve the mystery later. Is all well and good - but these notes are anything but subtle and if you do not meter thick board in front of the head, you know immediately what is going on. This is followed by 2-3 more "subliminal" Hints and if it ans big "coming out" is, the reader is already annoyed, he knows / the but since about 300 pages (-or even since the previous book).
I assume strongly that I can not be regarded as Sherlock Holmes and the signs in the book are simply too obvious and clumsy. What I find a shame considering the great world and its characters.
As a fan of Urban Fantasy these books are still a must have and one can above drawback easily overlooked because the history of their characters and their relationships alive and captivates the reader. With the big shock moments Cassandra Clare can not lure me, because these only bring reading fun if the reader does not expect it.