Diane Greco thinks (27 May) I slighted writers in Pomp. And, reading her refutation, I'm inclined to agree that she's right and I'm wrong.
But novels and stories have structural requirements -- and these are notes, so to speak, that must be hit in order for the piece to succeed at whatever it is supposed to do (according to expectations defined by the artist or the audience or tradition or whatever). For instance, in my novel, I know the first fifty pages must set out, in miniature, the moral universe of the book, and that there must be thirty really stellar pages just past the midpoint, where the moral crisis prefigured in the first big chunk must be resolved on pitch.
If I were to mount a defense (and it does, admittedly, smack of 'If it will appease her sorrow,/ I'll marry this lady today,/ And I'll marry the other tomorrow! "), I think it might be along these lines. Dan Brown is obviously a professional writer; The Da Vinci Code is a best-seller everywhere, it's spawned admiration and emulation and explication. He may not be a good professional, but Deivi Cruz isn't a good shortstop and nobody says he's not starting for the Cubs and therefore a pro. Unfortunately.
But back to the point, such as it is. In terms of pure craft, the Da Vinci Code is not impressive. Characters are inserted for patently formal reasons. They do things to advance the plot without motivation, and they decide to be bribed or unobservant whenever their natural behavior would obstruct the thrilling chase. There are so many buckets of exposition that we need an entire subplot to justify a second explicator.
This is not, to my mind, a genre issue. John LeCarre doesn't have these problems; he generally hits the notes. So does Patrick O'Brian. So, for that matter, does Stephen King. King wrote Carrie perched on a card table in his spare time; I think the Kings were living in a trailer at that point, and he got the idea from either being or talking to a school janitor. (Can't check the details, I'm on the far side of the world. Sorry.)
But, in the end, Diane is right.