I admit to a certain feeling of kinship with Dan Brown, sharing a hometown, knowing his family, meeting him several times. Even if none of that were the case, I think I would still have become a fan of his work, laboring manfully as it does to meld history and action. Sometimes it works and sometimes it doesn't, but I admire the effort. Brown's approach has generated controversy and criticism, some of it founded and some of it not. I will say this - like any obscure author, I could only wish to write something people loved or hated as much as his work.
For me, Robert Langdon is a bit too reliably heroic, his brain a bit too supercharged, like the love child of MacGyver and Indiana Jones. And I never bought Tom Hanks, especially a doddering, decrepit Tom Hanks, in the role. All of that said, Angels and Demons is my favorite of Brown's oeuvre. The concept and the characters are fresh, the template new from the fertile factory of Brown's mind. The book itself wrestles with some weighty ideas, and while it does so we are introduced to the author's finest character, The Camerlengo Carlos Ventresca (Patrick McKenna in the film. This deals with the book version, even if I use Ewan McGregor's image from the movie here.)
The Camerlengo is an utterly compelling creature, a man of passions and magnetic personal power. He is both angel and demon, a zealot whose true faith was in himself and his own destiny. His vision of the Church and its place on Earth was not open to discussion or modification by lesser lights. Like so many other visionaries and crusaders and would-be messiahs, his way, unvarnished and unadulterated, was the only way. And that hubris was his downfall, even as he came within a breath of total realization of his dreams.