Hmm, I quite agree about Dan Brown.
I remember that when the hype was getting really breathless over "The Da Vinci Code" I went out and bought a copy to see what everyone was on about.
The fact that my previous read had been Iain M. Banks' lastest oeuvre only served to enhance the feeling that I was reading a "Janet and John" book. The only thing missing was the "New word" footnote on each page.
When the court case over blatant plagiarism of "The Holy Blood and the Holy Grail" came up, my only reaction was "Funny, that's exactly what I was thinking after the first couple of chapters.".
So it's someone else's plot with a hero, villain and dolly bird dropped in, rewritten to appeal to the terminally thick.