This is the book version of the authors' 12-point presentation to demonstrate step-by-step that Christianity is true.
Reading this book as an atheist I found the first half of the book particularly hard going, where they attempt to demonstrate from first principles that God does exist. This is not because they tackle particularly difficult concepts, or because they write in a hard-to-understand way - they don't. Rather it's because the philosophical and scientific objections to their point of view are often dealt with in a rather patronising and smug way, sometimes missing the point of the objection. For example, a few scientific theories are described as "couterintuitive" or "against common sense", and therefore it takes more faith to believe them than Christianity. Unfortunately, as anyone who has ever studied Quantum Mechanics or Relativity knows, just because something is counterintuitive doesn't mean it's not accurate.
After about my fifth exaggerated reaction to something they had written (clasping my hand over my eyes, yelping out loud, etc), I thought to myself "this must be how it feels to be a Christian reading The God Delusion". The style of writing in The God Delusion can be patronising and smug at times, and simplifies theological objections to Dawkins' point of view. But just as I would highly recommend The God Delusion to anyone, and insist they force their way through the bits they don't like, I did the same with this book.
Once the authors have demonstrated to their own satisfaction that this is a monotheistic universe (and therefore Judaism, Christianity or Islam are the only religions that could possibly be correct) they then start to go through the bible and explain why they believe Christianity is true. At this point, I was very pleased that I'd managed to slog through the first half - because the second half was extremely engaging and made its point in a very accessible way.
The old testament and the new testament are both discussed, and their reliability assessed. The life of Jesus and whether he really was the son of God is also covered (in quite some detail), as well as the reliability of the Apostles and other witnesses. The whole second half of the book was a lot more convincing than the first half, and really gave me a much better understanding of Christianity (and Christians!).
Overall, I did find it frustrating to read - but rewarding. I would recommend to Christians, atheists, and those of non-Christian faiths as an insight into Christian beliefs. Will it convert anyone to Christianity? Possibly, but it didn't convert me.