The Lost Symbol works well as a thriller. However, it spends a little too much time trying to breach Dan Brown's version of Deism.
In this story, the famed "symbologist", Robert Langdon gets a call to urgently come to Washington D.C. to fill in for a lecturer who couldn't make it to a very important lecture. However, this turns out to be a charade to get him to help unravel some deep secrets held by the Masons. The plot goes through a number of different twists and turns, with plenty of impressive escapes before the world is saved. Then it rambles on for a number of chapters on philosophy.
Being a modern thriller, the hero runs in to a some archetypal government agents, and (of course) manages to get connected with a heroine who is at his side for much of the quest. He barely manages to escape many close encounters, but also manages to get caught a few times when we think he is on the verge of escaping. There is just enough variety to keep things interested without being too predictable (or too over the top.)
The Masons are portrayed sympathetically, and the philosophical ramblings seem to espouse the masonic view as preferable to mainstream science and religion. (However, you have to wonder how well that represents what the Masons really think.) Just about every Washington D.C. conspiracy theory imaginable finds its way in to this book, along with plenty of geographical details of the city. (This would make it interesting for anyone very familiar with the area.) However, where the book excels is in the action. Unfortunately, a little too much additional time is used to "preach", distracting from a good story.
Heaven's Ditch is a history of some of the key events in upstate New York in the early 1800s. The book interleaves a number of different events: the construction of the Erie canal, the story of Joseph Smith and the rise of Mormonism, William Miller and the adventist movement, Sam Patch and daredevil entertainers, William Morgan and the rise of the anti-Masonic movement, Charles Finney and abolitionists. It does not attempt to provide a general history of the area, but instead a history of these events that were in part enabled by the construction of the Erie canal. The book almost succeeds. It provides a nice overview of the spirit of the times. However, it loses focus, and provides both too little and too much detail. (It spends significant time wrapping up Joseph Smith's story in Missouri and Illinois, yet barely glosses over the enlargement and legacy of the Erie Canal.) The author tries to be objective in covering the events in the story. However, he does inject some of his views and color of the events. As a history, the book is week. However, it does tell an entertaining story that helps link together a number of key events that were happening in close proximity.
