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This book was perfect for me, coming from a non-catholic background. Since it does not read like a book laden with catholicism, I wasn't turned away by the language or structure of the book. Not once did I feel the author was trying to proselytize me (something sadly lacking in some other books about the catholic church). What I found was an honest, objective look at the papacy: there have clearly been good and bad popes (some, though very few, have been downright loathsome people), and there have been popes who were incredible men. This book is honest in its appraisal of the men who held the highest earthly order of the catholic church.
There is a slant, and the author hits you in the face with it, but not until the very end of the book. It is not laced throughout the text. Depending upon your perspective, it will either horribly offend you or surprise you with its candor. I personally found it refreshing.
In short, if you're curious about the papacy from a historical perspective, this is a good place to start.