Wasn't 'Angels and Demons' written BEFORE 'The Da Vinci Code'? Which means Dan Brown was still developing his powers as an author, so it's unlikely we'll see the later novel's 'extraordinary' prose, 'astonishing' plot and 'thrilling' character development.
But I reckon it will still read like he had the wikipedia guide to Rome open in front of him.
At a wild guess:
'Langdon walked across St. Peter's Square, distinguished from the territory of Italy only by a white line along the limit of the square, where it touches Piazza Pio XII. St. Peter's Square is reached through the Via della Conciliazione which runs from the Tiber River to St. Peter's. This grand approach was constructed by Benito Mussolini after the conclusion of the Lateran Treaty.
'It was only then, as he perused the menu in a family-owned trattatoria that he saw the reflected image of the lesbian assassin nun wielding the cold fusion assault rifle.'*
Word to Ron Howard and Tom Hanks - you gave us 'Apollo 13' for crissakes - why are you making this shite???
* If anyone has a couple of million burning a hole in their pocket I am willing to write the rest of my screenplay - complete with the lesbian assassin nun, the cold fusion assault rifle, prominent placement of the product of your choice (Coca Cola, Pepsi, the Shroud of Turin you name it, I'll cram it in between the roof-top car chase and the CGI sidekick), Dolph Lundgren and/or Jean Claude van Damme in a dirty green vest as the mitteleuropean action hero who dies a gory death at the hands of the Provisional wing of the Salvation Army, and a huge, deeply satisfying climactic explosion which will have me venerated by hearing specialists for years to come. Think Michael Bay without the taste and restraint but with gothic chanting on the soundtrack.