I generally like Brown's Langdon books, but this one left me Blah. I think I figured out why: 
 (view spoiler)[ At the conclusion, we discover that if Langdon had never left Boston, never gone through the events of the book...absolutely nothing would have changed, other than that woman who fell through the tapestry to her death would still be alive. The "plague" was already released. I felt empty, wondering what the point of the whole thing was. (hide spoiler)]