A Sceptic's Guide To Atheism is a rock solid reply to contemporary atheism and Peter Williams thoroughly dismantles some of the strongest objections that atheists have to Christianity. I stress that this is no ordinary book reply and is almost certainly the strongest critique I've come across. He takes on in detail, people like Richard Dawkins, AC Grayling, Daniel Dennett, Carl Sagan, Lewis Wolpert and Sam Harris. As other reviewers have mentioned, one of the unique aspects of this book is the immense amount of research that Williams has put into it. There are pages and pages of footnotes per chapter and he lists an astonishing amount of recommended resources such as books, online papers, videos, audio debates and some of his own essays. It is interesting to compare the amount of research in this book to the research done in recent New Atheist books. Another unique aspect is Williams' use of quotes which are mainly from atheists! This is not a downside as it may seem to some, but it allows him to honestly and fairly engage with critics of theism and to really get into their way of thinking and of course it prevents him from misrepresenting them. Although this is largely a book that critiques atheism, the author does not neglect to build a positive case for theism and does so in various ways (even though it isn't the main intention of the book).
If you intend to read this book it does help to have some background knowledge on philosophy and science as Williams does get into some complex and deep issues throughout the book and covers a lot of ground in each chapter. It would probably beneficial also, though not necessary, to have read at least one New Atheist books or at least be partially familiar with their arguments. A Sceptic's Guide To Atheism is informative, well researched and devastating in it's critique of New Atheism. If you are an atheist and are willing to challenge your own worldview or a theist looking for some unique and valuable apologetic material, I heartily recommend this book.
If you would like to read a more detailed review of this book, I have written one for my blog here - http://philosopherjosh.wordpress.com/2010/08/30/book-review-a-sceptics-guide-to-atheismgod-is-not-dead-peter-s-williams/