I saw Angels & Demons a couple of weeks ago, immediately after reading the book. I'm one who takes greatest delight when a movie closely matches its basis book, and in this sense A&D was a disappointment to me, at least I was less satisfied with it than with The Da Vinci Code movie vs. its book.
Sometimes the changes are simply stuff left out or truncated to make a reasonable-length screenplay, and that was for the most part the case with DVC. The theatrical presentation left out or shortened several critical points that rendered it a bit hollow in my opinion. But the extended BD version (close to 3 hrs long) put some of that back in and, again IMHO, was all the better for it. (With the BD one can pause and take breaks, so the length is not an issue like it is in a theater.) The extended-length movie much more closely matched the book at least in terms of the depth of the underlying information like Sophie's bloodline and Teabing's longer explanation of the holy grail as another manifestation of the "sacred feminine" in context with The Last Supper.
With A&D, the movie took departures that are not simply ommissions, tho' they may have been rooted in the necessity of shortening the screenplay. Two of those departures change the story line somewhat, and cannot be reversed in an extended length movie (which I hope will be what is eventually released in BD anyway). In my opinion, one very important part of the book (in which I actually found a personal epiphany!) was the Camerlengo's speech to the cardinals. That was truncated so much in the movie that the message was largely lost, and that also contributed to my disappointment. (That full speech could readily be restored in an extended version; it was not part of the main storyline in the book or movie but did contain a powerful message that this non-Catholic really took to heart.)
That said, A&D was a fairly exciting movie on its own and made an interesting "sequel" to DVC. Fiction to be sure, but it still makes you think "Hmmmm"...just like any well-crafted conspiracy theory should, and Brown is proving to be a master of that! vurbano makes a good observation about the relentless "explanations", but you might be able to ignore that aspect to better enjoy the storyline...
BTW - Welcome to WiSa...!