NDG  here in Chicago got in Escalation and Stronghold Assault yesterday and I've been really intrigued to look at both of them.
Escalation is Apocalypse-Lite. GW wants us all to own and play with Super-Heavies even if we don't play Apoc scale games, so they expanded the force org to include a 3rd optional category called Lords of War (the other two being Allies and Fortifications).

The goal is to make it legal to play these in standard pick up games without all of the fanfare and set up of Apocalypse. To balance it out, if you don't field a Lord of War and your opponent does you get a +1 to your Seize the Initiative roll. Additionally, an additional secondary object/source of victory points (similar to Line Breaker and First Blood) appears to give you a VP just for doing 3 Hull Points in damage to the Super-Heavy.

Its not like a typical Expansion book in that there are no Stratagems or other additional layers of the game to pick and choose from added. Instead, there's a Lord of War Warlord Traits table you can optionally roll on and a bunch of new scenarios to choose from, but it is made very clear that playing these models in standard rule book missions is fine, and these missions are just to expand your options for themed conflict.

Its a savvy move to try and sell big kits to people who cap their games at 2000 points. All of the data sheets appear to be the same as Apocalypse, and D weapons remain unchanged. This just allows you to access all of that information without owning the Apocalypse book.
Stronghold Assault is a much shorter book and is much more in the vein of Cities of Death and Planet Strike.

Once again they are trying to get you to purchase more kits, this time the scenery ones. It provides you with the data sheets for all of the Fortification related scenery kits and gives you new combos. It also introduces 3 new ones with no art/photos and thus, NO KIT TO SELL US. This was a huge surprise to me with GW's recent policy of not introducing army list options without kits.

Unlike Escalation which is clearly trying to get you to play standard 40K with Lords of War, this book is approached knowing full well that you're already using Fortifications in your games (at least Aegis Defense Lines anyway) and then gives you a bunch of new scenarios to play in order to play out Siege battles. So its kind of like Planet Strike without the grandeur and additional set up. You pay your points for your Fortifications, pick a mission, and play. Its not like learning a new system and all sorts of funky rules EXCEPT! The Building rules are expanded to make using the new kits even more clear.
From the 4th Edition 40K Rule Book under "Raid Missions". Raids used Sentries, Hidden Set Up, and Divided Forces. Other 4th Edition Raids included Sabotage and Ambush. There were also Breakthrough and Special Missions, each with their own FOC charts. Most players ignored these parts of the book I think. I LOVED those parts of the book.
This book plays into a certain nostalgia for me as it resurrects a handful of old scenarios like Strongpoint Attack and Break Through from the 3rd and 4th Edition 40K Rule Books. I always loved the scenarios in the back of the book more than the tired Standard missions you play all the time.

Overall, I think both books are really cool. I have a Baneblade and a Stompa kit waiting for my attention but I'm not sure they'll get paint just yet. If a plastic Thunderhawk was released beside this book, that would have been a different story. I'd probably be writing this while foaming at the mouth.

The book I was less excited for, Stronghold Assault, has wormed its way into my conscious however, and I think I'd really enjoy playing some Siege missions and I'm trying to think of events for both NDG and Adepticon that could possibly make use of this book. We'll see.

-Nick