There's a lot of really great information in this book, as well as helpful suggestions for approaching Muslims. For example, Chapman gives several reasons why the parable of the prodigal son and the Gospel of Luke are the ideal places to start in Scripture. He also gives helpful historical, political, and ideological context for contemporary Muslim thinking.
But the book falls flat in a number of ways. First of all, it's poorly organized and redundant. It's difficult to see a logical progression -- it feels like a sequence of tangentially related chapters, many of which cover the same material. It doesn't help the problem that the book is as long as it is. Nearly 400 pages, with a somewhat small font. I had to fight to keep my eyes from glazing over each time I turned a page.
It also suffers from a lack of clear theological perspective. In certain places, it seems Chapman is attempting to speak from the standpoint of (an absurdly broad and nebulous) "mere Christianity." In those places, he is unable to offer clear suggestions because he must be inclusive of all types of Christians. On the other hand, there are parts where he speaks firmly about inerrancy, penal substitution, salvation through faith alone, and so on. In still other places, he entertains the idea of inventing a new sacrament to replace baptism in order to avoid all the connotations baptism has in Muslim contexts. It's all over the place.
I would recommend What Every Christian Needs to Know About the Qur'an by James White over this one any day, even though it's missing some of the very helpful information contained in Cross and Crescent. It's much easier to follow, and written from a clear doctrinal stance that is able to provide specific answers to important questions. In the end, this book just wasn't worth the trudge.