I enjoyed it so much I read all Dan Brown's other books. No-one should judge him against any of the 'great' writers as he is writing a thriller, an erudite one perhaps, but a thriller nonetheless. Aside from the twists and turns of the plot, what is compelling is how much he causes you to question what is true and what is not. Yes the plot is preposterous but it is entertainment after all.
Angels and Demons, set in the Vatican, is even more preposterous but IMO is even better.
Digital Fortress and the other one about the meteorite are pedestrian by comparison