I probably don't even need to review Dan Brown's The Lost Symbol: you're either going to read it anyway, or you're not. If you're expecting something radically different from Brown's other novels, you may be disappointed, but if you want another installment of the Robert-Langdon-breathlessly-manages-to-solve-another-creepy-symbolism-based-mystery-over-the-course-of-a-few-short-hours show, this is your book. It clocks in at just over 500 pages, but as with all of Brown's books, it's a very fast read.
Brown's writing has improved but little since The Da Vinci Code, and unfortunately this book seems to have escaped much attention from whatever editors were assigned to it (as the later J.K. Rowling books appeared to as well). Some careful proofing could have cleaned up the prose fairly significantly and removed at least some of the eye-rolling moments (which included the spot where Brown mentions one character's “tiny black eyes” at least three times in three pages).
I found it necessary to have an Internet connection handy while I was reading this book, since while Brown is constantly describing artworks and architecture and other such things, his books don't include illustrations. I first read The Da Vinci Code in the illustrated edition, and found the added images incredibly useful; presumably one of those for this book will be forthcoming, but in the meantime prepare to keep Google at the ready (or trust Brown's descriptions, which I found were not always entirely accurate; he has George Washington dressed in white robes in “The Apotheosis of Washington” - the painting across the inner dome of the Capitol's Rotunda - while the painting clearly shows him wearing purple, for example).
Quibbles aside, this is a fun read, with some surprising twists and turns and a reasonably interesting premise (even if it is utterly improbable) and a fast pace. And I have to credit Brown for what seems to be a very even-handed and fair treatment of the Freemasons, the group at the center of the book's plot.