One thing I really liked was all the quotes and allusions to the Bible throughout the book; I felt that they definitely added to the story and made it more interesting. I also liked learning more about the characters' pasts and all the unanticipated twists that happened because of some character's obscure past. :-)
I think most people have already read these books (I would have gotten my hands on them earlier if there hadn't been so many holds at the library!), but if you haven't, I would strongly recommend it. Cassandra Clare skillfully weaves together fantasy, paranormal fiction, adventure, and more in this highly popular series.