Well, the subtitle probably should have been "why Christianity sucks and Islam rules". There are so many examples of Armstrong making questionable comparisons (the catholic v. sufi mystics being the most obvious). My favorite is at the end where she castigates the (christian) U.S. for the re-establishment of capital punishment as "not a sign of a spiritually healthy society". No mention of how decapitation and stoning are routine sentences in spiritually healthy societies such as Iran and Saudi Arabia.
Having said that, there is a lot of information in here. When I could parse the opinion from the facts I learned a great deal from the book. Which is cool. Armstrong just made it harder than it had to be.