Shannara:
I've tried to set something in the city of Haven, from Simon R. Green's books ...
Hawk and Fisher for the win! I
loved those books, and Green's sci-fi Deathstalker saga that came after. I never quite hopped on board with his magic-noir stuff though.
Green's world-building would lend itself fairly well to an RPG tale. The way that he alluded to the many villainous offscreen characters and factions, I mean. In those books, there would often be provocative names dropped left and right, not all of them made actual appearances as characters. It really gave the reader a sense of the setting, the grim tone of the city, but didn't really paint you into a corner with the details.
Completely made-up of course, but it wouldn't have been weird to see names like: The Prince of Rats, Jenny Machete, The Razor Twins, Our Lady of Stitches, etc.
I feel like a reputation game mechanic of some sort would have to be introduced in a tale like this. The protagonists would often win/avoid a fight without even drawing a sword (or axe!).
A withering stare down, and a few implied threats were enough to do the trick in a lot of instances.