Image by Simbe90 via FlickrI ripped through this in about three days, so it certainly kept my attention. Some of the running around D.C. smacked of National Treasure, but I didn't mind.
The trove of arcane historic trivia was almost overwhelming, but the new characters added to the mix. The whole thread of "Noetic" sciences seemed a bit forced, as did the epilogue, which seemed very preachy.
Some of the plot twists caught me by surprise, some didn't. I don't think Dan Brown fans will be disappointed, and I'm sure he'll make some new ones with this book.
Anyone who liked the earlier Langdon books will enjoy this one. I would rank this a slightly behind the other two novels, but definitely in the same neighborhood.