Dawkins is a scientist who also seeks to make philosophical points by extending Darwinian reasoning, which is his professional field. He is great (and as ever creatively controversial) when he sticks within the confines of his discipline, but outside of that I think he tends to go overboard. This book, an extended screed of militant atheism, is over the top even for me, a lifelong atheist.
His basic argument is that Darwinism proves that God – a super-intelligence of some sort that controls everything via supernatural powers – almost certainly cannot exist. The logic goes like this: though nature appears to be designed, evolution (i.e. Darwin's theory of natural selection) teaches us that ever-greater complexity arises out of incremental changes; if that is the case, as all evidence suggests, then a God-like designer would have to first be designed, which is impossible, given that nature begins in simplicity; the rest is misplaced wishes to impose a cosmic order (on everything and everyone) that doesn't exist. I get this and agree with it.
The question is, what should we do about it? Dawkins’ answer is to rail against the ignorant beliefs of the faithful in the most arrogant and angry manner he can muster. The entire book is a series of shrill denunciations, presented as (quite valid) academic proofs. This is exhausting as well as tedious and deliberately offensive.
As an argument, the book is also a poorly organized, sometimes too chatty, and self-serving in its display of Dawkins' erudition. Seeking to debunk as deficient everything that people claim religions can help, e.g. comfort in the face of death, Dawkins ventures into many realms without sympathy or much historical perspective. He also goes over a lot of the notions he had written about with great acuity in other books as he marshals evidence for his case. I think I have had enough of him.
That being said, at its best – when he is writing about science – Dawkins can be very good indeed. The concluding chapter, which doesn't offer a good sum up, becomes an essay on how our physical bodes have limited our commonsense perceptions in a way that only science can overcome. It is wonderful and I won't forget it, but to link it back to his purpose requires the reader to square the circle to get to the idea that it applies to religion – we project the faces of our parents on the sky, or some such.
Regarding atheism, my answer is: make your case, then so long as believers don't try to impose their beliefs on you, let them go their merry ways allowing for the possibility that their views may evolve over the long term. A branch of my family is fundamentalist Christian, some of whom are doubting the tenets of their faith because given how their lives have gone, they can no longer believe there is a moral order to the universe. I respect their struggle.
Though he can argue well against creationists (who will simply reply that Satan put dinosaur bones around to fool us) and better against "intelligent design" I think he hurts the cause of atheism more than helps it.