The other reviews here are quite comprehensive, so it will be difficult to add something new. However, I will try.
I have seen Craig in debate numerous times, read one of his other books ("Reasonable Faith: Christian Truth and Apologetics) and he is the best intellectually respectable defenders of Christianity alive today. Comparing his debates to this book shows that Craig has a wide range and knows how to argue at a level appropriate to his audience. Craig can talk to the interested public and academic philosophers alike. This book definitely falls into the second category (Craig did his first Ph. D on it) and it is aimed at those who want a comprehensive defense of this one particular argument for God's existence.
The book is divided into two main sections. A historical review of the argument as it was originally presented by various Islamic philosophers about a thousand years ago starts the book. I found most of the arguments here comprehensible because Craig had the foresight to put the arguments into a chart, so that you can visually see the progression of the ideas. For most readers, this material will be completely new. Islamic philosophers are rarely covered in first year university and courses on such topics are few and far between.
The second section is the modern defense of the kalam cosmological argument. Craig arguments are of two types; philosophical (using mathematics as his evidence) and scientific or empirical (using astronomy and physics as his evidence). The mathematics arguments are extremely difficult to follow and I think most readers will only understand parts of it. Some of his observations are as follows; even if an actual infinite exists in mathematics, it is generally thought that mathematical concepts have no concrete existence (this is something of a simplification, but that is unavoidable in the space available), that an infinite cannot be formed by addition and so on. I get the impression that the mathematics Craig uses (primarily set theory) is a simply a modern presentation of the Islamic arguments, which I founder easier to comprehend. The basic conclusion offered is that an actual infinite is mired in contradictions and thus cannot exist.
The second part of his evidence deals with astronomy, the Big Bang, thermodynamics and so on. Craig refutes the non-Big Bang models of the universe. The Big Bang model of the universe asserts that the universe began to exist approximately 15 billion years ago. The steady state model (which asserts that the universe is eternal) was refuted by empirical evidence in the 1960's while the oscillating model is confronted by major physical problems that make it quite implausible. Craig prefaces this section with a comment that some people find abstract philosophical argumentation too difficult and thus prefer the "concrete" sciences. Personally, I think that philosophy is better equipped, as a discipline, to address questions such as: Is the universe eternal? Did the Universe have a cause?
Briefly, near the end of the book, Craig defends what he rightly regards as the causality principle. The principle holds that whatever begins to exist has a cause. Craig presents the arguments of some other philosophers who attempt to show that this principle is self-evident or otherwise inescapable.
This is, without a doubt, the most difficult book I have read this year. Yet, it is quite rewarding. Craig successfully argues against all those who disagree with him and it is challenging to imagine a refutation of his position. If you have taken "Philosophy of religion" courses at the university level, you would definitely appreciate the book although some of the math-based arguments may be difficult to follow. I would only recommend it to people with a broad understanding of philosophy and or apologetics. If you would like an beginner's introduction on how to defend the Christian faith, I recommend, "The Case for Faith," by Lee Strobel (very readable and easy to understand), "Mere Christianity," by C.S. Lewis (a classic defense of Christianity, but it is quite short and not quite as rigorous as I would like). For a more in-depth defense of Christianity that covers both the existence of God, miracles, and Jesus Christ, J.P. Moreland's book, "Scaling the Secular City" (which I have reviewed) is bar none the best. Craig's book, "Reasonable faith," is also fairly good.
P.S. If you intend to offer a substantive critique of the argument, you must undermine the philosophical and scientific arguments for both of them independently establish the beginning of the universe, one of the key elements of the argument. One of the reviewers, George Tucker, "refuted" the argument in less than 100 words without addressing any of Craig's evidence. This is a poor attempt to refute an brilliantly argued book.