This as many of Dan Brown's books is intrinsically interesting, not because of the story, plot development of characters, but instead because of the place the story takes place in. 
 Florence was the first European city I visited when I was 16 years old. I have very fond memories of the city and the 4 months I lived and studied there, so it shouldn't come as a surprise that the parts of the book I liked the most were in the beginning when Robert and Siena escaped through some of the most touristic destinations, like the Boboli Gardens, Palazzo Vecchio, Battistero di San Giovanni, etc. Even when I thought that the secret scape routes although real, where unconvincing because of the sheer number of tourist at everyone of these places. 
 The middle and the ending of the book I found equally hard to believe, and that the author wanted to make a plot twist just for the sake of it, that is probably the reason they changed so much the story and ending in the movie.