Call Forth Darkness is another solid adventure, although personally, I liked the opening installment just a bit better.
The PDF, like it's predecessor, is beautiful. The layout, colors, and artwork continue to be very impressive.
The Farholde Gazetteer in this book does a lot to bring the setting to life, which I think is important in an adventure path such as this one. The more the PCs realize that there is some history and culture behind the targets they eliminate, the more the fact that the PCs are villains is really brought home.
The article on evil organizations and minions presents a subsystem for managing minions that I wish were available in slightly more generic form for non-evil groups that also have followers. It's nice to have some guidelines as to what all of those “not quite combatants” can do when you take the time to actually be a leader.
An interesting addition at the end of the adventure is the exploration of other ways to structure the adventuring party and frame the AP based on specific themes (i.e. the whole party is clerics, the whole party are wizards, no one is a spellcaster) and what needs to be done to fit that theme. It's not overly detailed, but it's nice to see these musings and I'd like to have seen this kind of thematic conjecture in some of Paizo's adventure paths.
Now, for the adventure itself. When I say I prefer the first installment, it's not a matter of quality. It's from the GM expectation point of view. This adventure could be great or it could nosedive, because while it is a brilliant premise and laid out about as well as you could for this kind of concept, it really depends on the PCs picking up the ball and running with it.
That is true to an extent in the original adventure as well, but without a direct authority figure nudging them as much as they might have had in the first adventure, while the ultimate objective is clear, the compelling bit in the middle might not be as cool if the PCs don't get the vibe that the adventure is sending out (i.e. if they treat this as a dungeon to clear out rather than one to dominate).
One last nit pick that I will try to throw out there without spoiling too much. I love the security point concept, but wish it did more than it does. The payoff isn't quite as tangible outside of the metagame rewards.
All in all, recommended, and greatly recommended. Just pray that your players really relish being villains and not just evil characters.
[4 of 5 Stars!]