While much of the evidence in this has been debunked since it's writing, and most of the research has been called into question, this is an interesting book nonetheless, with much more depth, twists and turns than The DaVinci code, which stole many of these author's ideas. There are many concepts in this book, some are very dubious, and others seem downright plausible. If one approaches this with the right spirit; which is to say, with an open mind, but with the desire to do lots of independent research, it can become a wonderful real life detective story. At worst, you could take it as an interesting mockumentary-style story, and still have a pretty gripping tale. (there is a long stretch on geneology in the middle that lags quite a bit, but stick with it, it's worth the payoff.) At best though, it is something that will make you question what you've been told, and try to do a little independent thinking on the matter.
Read this book, absolutely, if you have any interest in religious history, but take it with a grain of salt. I hope to see someone pick these ideas up again, dust them off, and do the work that the authors didn't, giving us a real chance at looking at some of these theories honestly