"The Rebbe, the Messiah and the scandal of Orthodox indifference."
by Prof. David Berger
This is a book analyzing the Chabad movement which despite it's positive influence in returning people to the faith, they are causing massive problems with issues concerning the Rebbe being the Messiah, and the like.
The book is really interesting, and ofcourse there is a response to this as well, so check that out too to see both sides of the story.