OK, I've read through Stronghold Assault now...
Some thoughts:
1. This book makes buildings make so much more sense. I think that everyone should immediately start using the building rules from this book to cover the aegis lines, bastions, skyshield landing pads, etc. Honestly buildings before this book were a half-baked ruleset and I bet if you went to 20 game stores and saw how people were treating a blast landing on top of a unit on top of a bastion's battlements, you'd see them play it 10 different ways (does the building get hit? can battlements be damaged without the main building being damaged? etc). And let's not even start with the Skyshield pad.
2. The new fortifications (Firestorm REdoubt etc) have different rules with fewer holes in them (and more options) here. The redoubt actually says that 6 people can fire out of the 3" wide firepoint... makes a lot more sense than just treating it as a normal firepoint.
3. I don't think this book does anything to mitigate D weapons. Void shields won't do anything to stop D weapons. All you need to remove a void shield is to glance av12. So, you shoot an autocannon at it or something, the shield goes down, and THEN you shoot your D weapon. So you're spending 25 pts or so to make someone burn enough firepower to glance av12 once, that's all.
Basically, I love this book, except for the D Weapons. Nothing else in here screams "scary" to me, and it's all useful.