I like the world, but this book? Not so much. I have previously seen both the film (which I didn't like) and the TV show (which was very enjoyable), so I thought I would give the series a wack, but I felt that the way the book was written just didn't sit well with me, and reading this didn't really add to or enrich my understanding of the story in the way I expect an original text to do. 
 Overall, there were a lot of stylistic things that grated me through the book. There was a lot of information dumping, not a lot of character development, weird descriptions... she does this thing where she describes either the colours of everything or really odd things that have no relevance, like the clothes people are wearing, while not really succeeding at describing what is happening, such as the battle sequences/fights. I couldn't imagine a lot of the action sequences at all, and I frequently even had no idea how many characters were present - like in the final "battle", I had no sense that it was of battle proportions (at least in a sense that it involved more people more than the little fights beforehand) until she started citing the "sounds of the battle" and using terms to make it seem like a military operation halfway through the chapter. 
 I enjoy the idea of the world, but I can't say I'm a fan of the way this was written. I might give the Infernal Devices trilogy a go, since I know she wrote that after this series and had hopefully worked out some of the kinks in her writing (it is a debut novel after all), but I don't see myself continuing with the Mortal Instruments books. I'll watch the TV show though!