I am not a good judge of literary merit by any means, and I admit that I don't have very refined tastes at all when it comes to literature. With that said I do very much like Dan Brown's novels. To be honest they are all very formulaic and similar to each other, to the point where when you're reading the last one of his 4 books you pretty much know who will end up being a bad guy and who will not. From his style I can certainly see how those of higher tastes would scoff at his writing. But I'm only into reading to be entertained, and his novels get the job done for me.
You could probably guess that my other favorite books are the Harry Potter series, another popular, yet discredited series. But I also like His Dark Materials which seems to get a decent amount of praise.
