21st) Favorite RPG Setting
Freeport: The City of Adventure, by Green Ronin Publishing.
I love world-building, so I tend to prefer running games set in worlds that I've created myself rather than investing the time and money needed to acquire and learn a commercial campaign setting. The one meaningful exception to that general rule is Freeport.
At the time that I discovered Death in Freeport in my FLGS in late 2000, I was already considering using H.P. Lovecraft's Dreamlands (by Chaosium) as a setting for my first attempt at a D&D Third Edition campaign. Death incorporated pirates, serpent people, and the Yellow Sign, which made it the easiest sell any module has ever been for me. By the time that the rest of the original Freeport Trilogy was published, the city had become a setting that I was dedicated to following.
As delicious as the Trilogy was, it and the Freeport products that followed did have some niggling issues that prompted me to start producing unofficial fan errata for the line, which I posted to the Green Ronin forums. A few years later. this ongoing labor of love led directly to me making a pitch to Chris Pramas, the company's president and Freeport's creator, to update the Trilogy to the v.3.5 revised rules set. He accepted, and I became an official contributor to the setting.
I remain a vocal Freeport fan boy, and am currently running my third Freeport campaign. Not too long into this latest campaign, Green Ronin announced a Kickstarter for a new city book using the Pathfinder rules, which led to me converting my game to Pathfinder a few months before that sourcebook finally came out (around the beginning of this year). This new Freeport: The City of Adventure is easily one of my favorite RPG products--it's a shiny and massive new version of a dearly beloved old friend.