I would not claim that The God Delusion is a very original book. Most of the arguments and discussions in the book have appeared elsewhere before. However, The God Delusion is a comprehensive book which I think covers most the relevant arguments and discussions concerning science and religion. One influential (fundamentalist?) blog that I read recently complained that atheists cannot decide whether to attack religion because they think it is false or because they think it lead to evil. My response is that, religion should be criticized because it is plausibly false and because it is a source of evil. It is not a good defense to point out that your stance can be criticized from several different perspectives.
In the first chapter of his book Dawkins defines what he means by God. After all, God is defined in very different ways depending on who you ask. For example, there are many people who see God, not as an omnipotent, omniscient man in the sky, but rather they claim that God is the natural laws, or God is in everything. Personally, I think that semantics (the meaning of words), in essence is a democratic endeavor. I think that a word means what most people think it means. If you are not happy with that then come up with a new word. In any case, Dawkins makes it clear that he writes about the God as he is defined in the religions of Christianity, Judaism and Islam i.e. the God in the Old Testament (Yahweh).
Why should we respect a religious hypothesis more than any other hypothesis? That is the next issue brought up in The God Delusion. In my relatively short career I have only yet been part of one article submission. The way it works is that when you send in your article to a peer reviewed journal, the editors will read it and possibly send it right back with a "we won't publish this crap" note attached. If you are lucky the editor thinks that your article has a chance of being published in their journal. If so, the editor sends the article to two or three reviewers, typically your worst critics. The reviewers read the article and send their comments back to the editor. They also say whether they think the article is good enough to be published in the journal or not. After all these turns which usually takes two or three months (sometimes more), you get your article back along with all the criticism and ad hominim attacks (which occur every now and then) and more often than not with a negative response. Then, for a couple of weeks, you feel devastated and contemplate whether you should perhaps start working with garbage disposal or something else that suits your mental capacity better, and then you get back on the horse and send your article to a less prestigious journal.
"A widespread assumption, which nearly everybody in our society accepts - the non-religious included - is that religious faith is especially vulnerable to offence and should be protected by an abnormally thick wall of respect, in a different class from the respect that any human being should pay to any other."
I could not agree more. To criticize religion in the same fashion that scientific discoveries are criticized is completely taboo. I think this is strange because as I see it believing in a God is no different from believing that a classically conditioned memory trace sits in the Purkinje cell in the Cerebellum. Of course there is one important difference. Religion is often much more a part of a person than is for instance a scientific hypothesis. It is probably easier to really hurt someone by criticizing their religion than by criticizing something else, and I think one should take this issue into account, though not to the extent that we do today.
To illustrate the reactions that can occur when religion is criticized, Richard Dawkins, writes about the Muslims reaction to the cartoons that were published in Jyllands Posten. Sure they were probably tasteless and all that, but compared to the way Richard Dawkins was depicted in South Park (season 10, episode 12), it is nothing (I am a big south park fan by the way). In response to the cartoons in Jyllands posten one (fundamentalist) Muslim responded in a tragicomic fashion:
"Behead those who say Islam is a violent religion'."