A very successful and interesting book in the Religious Book genre is "Autobiography of a Yogi" by Yogananda. It is full of interesting stories while it painlessly explains much of general Yogic Philosophy. It does fall down somewhat by not specifically explaining the specific Yogic Technique of the Author's particular Organization... I suppose they would hope people would join up in order to learn the details. But the book is good as an overview.
The best book I have read that attacks a Religion is "Confessions of a Justified Sinner" by James C. Hogg. It was written in the 19th Century and the author took the format of being a journalist uncovering actual documents, which actually fooled much of his reading public. He was attacking Presbyterian notions of Predestined Election. The book is weird and haunting and unfolds with psychological insights that were half a century ahead of their time.
The most fascinating Catholic presentation I have read has been "Life of Jesus" in Four Volumes, the Blessed Anne Catherine Emmerich, who was Catholicism's foremost Seer and Visionary. The "Life of Jesus and History of Redemption" takes you from the Creation Story, through the Old Testament, through the Life of Jesus with a extensive explication of the Role of the Blessed Virgin. Volumes 2 and 3 bog down a bit... the first Volume could really stand alone.
The best publishing house I know of is Tans Books, for their catalogue of books on Catholic Saints, but it is better to order from Barnes and Nobles who delivers faster than Tan Books, but carries the same stock. I couldn't decide on which is the best Saint book. There are a few good ones. Saint Anthony of Padua, Saint Bernard of Clairvaux, Saint Vincent Ferrer, Saint Francis of Paola, Saint Joseph of Copertino.
The best single book on the History of the Marian Apparitions is "The Last Secret" by Michael H. Brown. He is best at presenting a great number of Apparitions in context to what their purpose throughout History may have been. and he is a polished author, which makes the book easy reading.