I really liked the story in this book, and really disliked the magic system.  The magic system was so core to the concept, and so contrived feeling that I really couldn’t take it seriously.  I especially thought the immunity was contrived, and in the end not all that important.  Normally when there are powers like this in a book I think about what I’d do with them, but the system was contrived enough that I couldn’t think about it.