Pathfinder has always had a healthy dose of Lovecraftian elements, but this adventure brings them all together, and initiated what I hope to be an ongoing collaboration with the folks at Chaosium (makers of the Call of Cthulhu game). Some background, first: Carrion Crown is a six-issue adventure path. This issue is the fourth issue, and is designed for 9th level characters. Each adventure path is intended to advance characters 3-4 levels.
The Carrion Crown adventure path is Pathfinder's horror-themed campaign, starting with Haunting of Harrowstone (the ghost story), then Trial of the Beast (a Frankenstein's monster themed story) and Broken Moon (the werewolves and zombies story). Wake of the Watcher is a clever twist on the Shadow over Innsmouth idea, but with many other interesting things going on. However, more than just an adventure, it's also a resource for any Pathfinder game. It contains a tour of the "Old Cults", a loose collection of Lovecraftian cultists that were introduced in Pathfinder Chronicles: Faction Guide, expanded to cover each profane elder got to whom they dedicate their worship and sacrifice their sanity. It also has a bestiary of Lovecraftian creatures for use in any Pathfinder game.
Overall, it's a well-crafted adventure and source book that brings the Lovecraftian horror genre to Pathfinder in a big way. Highly recommended.