I know what you mean... reading the book first and seeing the movie. It is most of the time a disappointment. I read the book Witness and then saw the movie, I could not recognize the people who were cast in the roles,even though they were amazing actors.
I have just started reading the Da Vinci Codes. My son bought the book when we came back from Europe,along with a satire of the Da Vinci codes published in Italian. We bought the other one in Italy.
Well, I know the movie is coming out in June and there is already a lot of controversy. So far, I read the three first chapters and I trying to figure out how in the world the actors who are cast in the roles will ressemble the characters. We shall see and Ron Howard is an amazing director.