The two best observations I've heard about Dan Brown are:

a) One thing he does very, very well is write a good plot that makes you curious enough to want to know what happens next. Unfortunately, the language he uses to write ABOUT that plot sucks dingo kidneys. (Personally, that would be enough to put me off, but I am much more persnickety about the quality of the writing than most other people -- to the point that it's almost a fault. So I definitely know that "but that's just me".)

b) An anecdote -- when the Da Vinci Code movie was coming out, some friends tried to round up a bunch of us to all see it together. One of our friends -- a hard-core Jesuit and highly literary type -- insisted that he read the book before we all saw the movie. So he borrowed it from one of our other friends.

Except that after he read it, he returned the book and said, "I don't want to see a movie made out of this crap." And thus he sat our movie night out in protest.

(In Dan Brown's defense -- that friend is even more particular about writing than me.)