In the Abyss was the second full adventure published for Planescape, and firmly established the Doomguard faction as one of the bad guys. While the Sinkers were a part of The Eternal Boundary, they were as much a victim of circumstances as all of the other factions involved. In the Abyss put the Doomguard’s alliance with the tanar’ri front-and-centre in the form of the Ship of Chaos. It also for the first time put the player characters square in the middle of the eternal conflict between the tanar’ri and the baatezu, and forced them to make a major choice: honour their contract with the baatezu to turn the Ship of Chaos over to them, or disable the ship to keep it out of all fiendish hands. Of course, if they’re not quick enough, they might end up lucky to escape with their lives!
Updated 31 May 2015: Added The Fourth Door: A Reality Beyond
Yet another adventure anthology, Doors to the Unknown involves the players in the politics of Sigil more than most other adventures. There’s a nice strong link between each chapter as well as a rough timeline that allows the GM to put other adventures in between each chapter. There are some weaknesses in the adventure (for example, there’s no indication that the players need to take the Rod of Mercury from the gearwork golem in the Thuldanin junkyard) but they’re nothing a good GM can’t work around.
Updated 9 Jun 2015: Added Chapter VII: Recruiters
The first of several adventure anthologies published for Planescape, Well of Worlds is a collection of nine short, un-releated adventures of varying quality. Some of the adventures set the seeds for later encounters and adventures, and the seventh adventure “Recruiters” includes a brief call-back to Green Marvent and the Illuminated from The Eternal Boundary.
The first Planescape adventure, The Eternal Boundary help set the tone for the later adventures and the setting in general. There are a few inconsistencies and some rough patches (many players have difficulty jumping from investigating deaths in the Hive to sneaking into the Mortuary) but overall it’s a good start to any Planescape campaign.