I read the books before seeing the movies in both cases (I don't think I even knew A&D was being made at the time when I read the book). Honestly I thought Da Vinci was the better movie and A&D was the better book, though they were both enjoyable enough movies.

The problem with A&D is that a lot of the book is puzzle-solving and dialogue, and they had to sacrifice a lot of the puzzle-solving process in order to fit all the actual action stuff into the movie, so you didn't really get a lot of the "oh, so THAT'S what that means!!" moments that you do in the book.

Also they kept in the utterly ridiculous "we can get from one end of Rome to the other in less than fifteen minutes!" that annoyed me so much about the book. I'd even say it was worse in the movie.

All that said... they were both quite gorgeous movies, and entertaining enough. I don't think I'd buy them for myself, but I'd keep 'em if I got 'em as gifts.