Summary. The notion of God is horsefeathers
Dawkins addresses the existence of God (an omnipotent, omniscient creature that takes a personal interest in human beings) as a scientific question, albeit one unlikely to acquire a scientific answer. He examines all recorded arguments for the existence of God, one by one, and fully debunks them.
Dawkins shows that no thinking person can believe in God, asserts that people who believe in God deserve no intellectual respect for that belief, and points out that Sunday school is child abuse. If you have a personal favorite argument for the existence of God, send it to me, and I'll send you chapter and verse in the Dawkins bible where you can find out why your personal favorite amounts to a childish fantasy.
Of course, plenty of smart people believe in God, but "smart" and "thinking" are two different things. Plenty of smart people think they're Napoleon, too. They're delusional. What makes them delusional? Dawkins has no definitive answer, but throws out a few ideas (clearly labeled as conjectures), one of which is that humans who didn't firmly believe the instructions of their elders, died more often than they lived. So, natural selection led to creatures inclined, as a class, to continue to believe throughout their lives whatever their elders told them, regardless of any objections their intellect might conjure up.
Dawkins does not assert that God does not exist. He says that thinking people must assign a low probability to the possible existence of God and must admit that there is, so far, no credible evidence in favor of the possibility. The assigned probability must be so low, in fact, that it is inaccurate to describe the thinking person as an agnostic. We don't fully preclude on a scientific basis the existence of witches, goblins, and leprechauns, but we are not agnostic on those issues.
Dawkins also advocates discussing religion in the same way as any other intellectual idea. No more "respect for beliefs." Belief in God deserves no respect, and respect shouldn't be offered. Of course, one must take care. Telling a person who thinks he's Napoleon that he's not Napoleon is usually inhumane. It disturbs a worldview carefully constructed by the delusional person to protect himself from something even worse than being a raving lunatic.
Summary. Even if the notion of God weren't horsefeathers, religion would be bad
Hitchens assumes you've already gotten past the God delusion. He focuses on the negative effects of religion. It's a horrifying list, but on the whole edifying, in a truth-will-set-you-free kind of way.
Summary. Religion has always been horsefeathers ... now, technology renders it intolerably perilous
Religious moderation combines secular knowledge with scriptural ignorance. Fundamentalists cause most of the problems, but moderates facilitate them by refraining from serious criticism under the guise of toleration. This guise is a luxury that is antithetical to human survival. It must go the way of alchemy and the stoning of blasphemous seven-year-old children, or we're all dead meat.
The Four Horsemen video