Just got my copy yesterday, and from what I have read so far, I am very impressed. I'm only about 20 pages into this 112 page adventure, but it is a campaign length adventure/series of adventures.
SPOILER BELOW
In a nutshell, a wizard gets a powerful item which she believes is for planar communication, but in actuality summons outsiders. When she accidentally summons a succubus, the demon defeats the wizard, takes the item, and flees beneath the city of Grey Citadel, where she plans to use the item to summon other demons to form her own demonic court. Interestingly, this succubus is a criminal in the abyss, and is very reluctant to summon demons she doesn't know due to the chance she might be discovered. The succubus then seduces an upstart rogue and has him form a gang of criminals that can work for her on the surface. This rogue is also gathering materials for use with the summoning item, and he and his cronies will likely come cross-purposes with the PCs. A wandering blackgaurd has also come to the city and is investigating rumors of demonic activity so he can pledge himself to a worthy evil patron. At the same time, another adventuring party is in competition with the PCs, which could lead to some interesting role-playing. In order to come to grips with what is going on, the PCs are going to have to do quite a bit of detective work, which pays off by giving valuable info that provides clues to some secrets and encounters later in the module. If the PCs miss some of the clues- they WILL miss the secrets later on. I'd recommend this one if you are looking for an adventure heavy on role-playing and with interesting puzzles and combats.