Angels & Demons - I find it hard to judge movies based on books if I read the book first, because it's difficult to separate the two and judge the movie on it's own merits as opposed to just comparing it to the source material.
I liked the book Angels & Demons quite a bit. It was exciting, fast paced, intricate, twisty and full to the brim with interesting shit going on all the time. But lets face it, there was a fair bit of ridiculousness with that helicopter escape and a LOT of people. Those are just two of the things that the movie changed - the reporter, camera man and director of CERN were all absent from the movie and Langdon never got in the helicopter so he never had to jump out and use the windshield cover or whatever it was as his makeshift parachute.
I knew they wouldn't make the Hassassin a Middle-Eastern man because that would be needlessly inflammatory so they turned him into an American (I think - at one point I detected a slight accent but then it was gone so I can't be sure) hired gun, in it solely for the money. The dead researcher was not Vitoria's father in the movie so they just went ahead and let her find him to minimize the drama there. And speaking of CERN, Langdon never even sets foot there in the movie, rather it's the Vatican that requests his help to find the missing Prefereti and the antimatter.
I could go on all day mentioning what was changed and arguing whether or not the change was for the better but the truth is, it doesn't matter. The book and the movie are two separate things and on it's own merits, I enjoyed the movie a lot. It was appropriately paced, it was well thought-out. Suspense, intrigue, action, drama - that's really all that are necessary in a movie like this I suppose and it delivers admirably.
The one quibble I won't set aside though, is why they changed the main Cardinal's name from Rossi to Strauss and then made another random Cardinal Rossi. It's certainly not a big deal and Lord knows that Armin Mueller-Stahl did a fantastic job as Strauss but could they not find any actors of Italian descent to cast and keep the name Rossi? Also, in the book I found Inspector Olivetti less than sympathetic while the Camerlengo seemed to be a protagonist the whole time. In the movie, the Camerlengo (Ewan McGregor) is kind of a douche and Olivetti (Pierfrancesco Favino) is awesome. It was disconcerting.
Damn it! I tried but I just can't seem to talk about the movie without talking about the book. Oh well. They're both worth your time I suppose.