First, there is a clarification that the Citadel Real of Battle game board is classed as open terrain for gaming purposes. All tests for moving through terrain are as before, but it is now a simple minus two to your charge result when charging through terrain. Models in ruined buildings receive a 4+ cover save even if they are not 25% obscured. There is no mention of Area or Lethal terrain?
Craters now only offer a 6+ cover save, although you gain +2 if you go to ground. Whereas Rubble is now listed with a 4+ cover save, even if you are not 25% obscured. There is a huge amount of terrain features that are no longer listed in this section, area and lethal terrain as already stated, along with wild undergrowth, forests, jungles and woods, rivers, lakes and pools, shield generators and fuel reserves! Mysterious terrain is totally gone from the book, with them only being used if you have a datasheet with you citadel terrain!
The book then quickly moves onto buildings. The large buildings section in the previous edition has been reduced down to just four pages covering all the usual building basics, there is a section to clarify who is controlling a building and how to claim them. Now I have to be honest and say that I have only scanned the buildings section. I will revisit buildings at some point, but I really want to move onto the missions and find out what they are all about, which is coming up next!