Despite all the respect that you feel for the man responsible for bringing you masterpieces such as The Lost Symbol and The Da Vinci Code, the latest book from him features a lot of coincidences (slightly unnatural but interesting enough to continue reading). It's slightly difficult to believe Robert Langdon would fly to Washington DC on a private jet quickly without talking (confirming) with the man who invited him. There are instances in the book where fathers do not recognize their sons. Dan Brown's characters talk to each other in complicated paragraphs, not like usual conversations that we (real people) have with each other. The hero of the book has a bad memory, which suddenly, turns good in one scene... unexplained.
A Different Kind of a Writer
Let's accept one fact - Dan Brown is a different kind of a writer who doesn't care about creating realistic conversations or scenes or even characters. But then, even his readers don't care. The reason is, he is too good at something which he is good at (hopefully, this sentence is clear enough). He is more like a natural puzzle creator who expertly accompanies you as you walk through it with him. He is expert at getting through to suppressed history and then mixing fiction with it, and then questions the conventional wisdom with his smartly crafted queries.