While I've disagreed with Abanes' conclusions in other writings ('Harry Potter and the Bible'), the information he presents in 'The Truth Behind the Da Vinci Code' is the same data provided in numerous other books published to answer Dan Brown's flaw-riddled conspiracy theories.
The reason I recommend this book above the others that I've read ('Breaking the Da Vinci Code' by Darrell Bock, 'Cracking the Da Vinci Code' by Garlow and Jones, 'The Da Vinci Deception' by Erwin Lutzer, and 'The Da Vinci Code: Fact or Fiction' by Hanegraaff and Meyer) is that the information here is concisely presented; Brown's claims are quoted verbatim from 'The Da Vinci Code' and reproduced in shaded boxes (with page references), followed by the facts which contradict Brown's claims.
Abanes' book is also the only among these volumes I've already mentioned which deals with the person of Leonardo da Vinci to any degree. Da Vinci's own writings tell far more about the Renaissance Man's religious convictions than Dan Brown's imagined "secret messages," and those historical documents are helpfully quoted here.
Again, the facts that Abanes lists here are available in many other books on this same subject, but I recommend 'The Truth Behind the Da Vinci Code' specifically for those who want to learn as many of the facts in as short a time as possible (it's a quick read, at 96 pages with footnotes. Those who care to do deeper research can easily begin an investigation of their own starting with these footnotes, or with some of the lengthier books on the subject.
For the individual who wants to learn what's wrong with 'The Da Vinci Code,' there's certainly no shortage of information available.