Harris makes some excellent arguments and insights, and brings to light many important facts about the World's major religions that all "non-believers" should be aware of. Unfortunately, however, he oscillates dizzyingly between truly incisive reasoning and scholarship, and vitriolic sarcasm and outright insults levied at religious followers.
Truly interesting and scary revelations, such as the fact that the Bible, Qur'an and most other books at the center of a major religion explicitly require the faithful to seek out non-believers and kill them is unsettling, to say the least. The fact that these books contain not one, but usually dozens of such edicts is eye-opening. Actually reciting every single such edict from the Qur'an, however, is a bit much, and constituted at least 8 minutes of my audiobook version. OK, I get it.
The basic theme of the book is that letting go of the need for proof in order to believe a proposition -religious or otherwise- is more dangerous than most non-religious people realize. That beliefs based on evidence must prevail over beliefs based on faith or we are all likely doomed, because faith-based beliefs are invariably mutually incompatible and require believers to destroy the "incompatibilities". Wow. Scary, interesting and well-documented. All religious people are, in so many words, irrational at best and insane at worst? That was unnecessary.
Most non-religious people are aware that virtually all religious texts contain some truly bizarre passages, and often internally contradictory ones, so normally this would make easy fodder for rational criticism. Harris, however, does a superlative job of elucidating just how truly bizarre and contradictory many of them are. Unfortunately, he then sarcastically and unnecessarily equates such beliefs with beliefs in unicorns and sea monsters. Why? The facts themselves are more than enough.
Harris makes some truly valuable points (though I don't agree with all the details, particularly with respect to US foreign policy). I just wish he had presented them with a little more detachment...
Still, read this book.