I jumped on the bandwagon and bought a copy of Dan Brown's The Lost Symbol when Amazon reduced the price to £4.99. I've read about 200 pages so far and the story is good. Yes the characters are a bit two dimensional and some of the writing is a bit clunky but it's a good story - which is what it's meant to be.
I can't actually understand why so many people say it's rubbish and shouldn't be published. Why not? I've certainly read worse books than his and it's not as if it's encouraging people to commit crimes or take part in dangerous activities. It's the fight between good and evil as depicted in James Bond, The Lord of the Rings and Harry Potter. The plot is not original - but then there's no such thing as an original plot since there are only 7 basic plots.
Maybe he hasn't got the factual details right - who cares? This is fiction not fact, guys, and if you want fact you would not expect to get it from a novel. Authors distort fact to fit the purposes of their plot. If they were writing non-fiction that would be different and they could be legitimately criticised if they got a fact wrong. Many people don't seem to realise publishing is a balancing act. Get a sure fire winner like this and you might be able to afford to publish books which are aimed at a narrower segment of society. Look at Bloomsbury's output now. They can afford to publish books which appeal to a minority because they've got all the money coming in from Harry Potter. And they've had commercial successes with books which at one time would not have been regarded as commercial at all so there are winners and - oh yes, winners - all round.