Quick review: Didn't enjoy this nearly as much as the first two books. Enjoyed it more than The Lost Symbol. The pacing wasn't very great, and I remember speeding through the first three books wanting to keep reading. But there was a lot in here that I enjoyed, even if I felt it wasn't as strong of a story, for this genre, as I've seen Brown bring with his Langdon books.
I'll probably keep going in the series if Brown writes more, though I don't have high expectations that it'll be more than what fans have grown to expect at this point. A good read, but nothing ground-breaking.