I understand framing the information in the form of a conversation between friends, but the dialogue was unrealistic. However, the information is sound. Sources are cited clearly, and anyone can go double-check any claims made in the book.
I also appreciate that this book does not degrade or insult Dan Brown’s work of fiction. It’s clear that McDowell appreciates a good story, and recognizes the merit of Brown’s book as a good story overall. It is obvious his only intention was to point out the factual holes in Brown’s fictional story, which I think is important. While fiction is usually very well researched, it is still fiction, and I think we often forget that fact, and it behooves us to check things out for ourselves. This resource is a good tool for that.
All in all, if I wanted a resource to hand to someone that does a good job simply separating fact from fiction in The DaVinci Code, this is one I would use.
For those interested in more depth, I would turn to other sources.