The scale goes from 0-10. 8-10 is a Normal game, 4-7 is a fair Theme game, and 3 or less is a Bastard game.
Example setup: NewD3
Example setup: 09:12
Example setup: 2:2:9
Slightly Unusual. A setup that barely isn't Normal. Usually either a global mechanic in an Open setup, adding a variant role (as in the former Normal greylist), or flavor shenanigans on a Normal platter.
Example setup: Noughts and Crosses Mafia
Low Theme. A setup that definitely belongs on the Theme side of the scale but doesn't go all out on Theminess. Something like BooneyToonz with all the flavor shenanigans that entail, or an otherwise Normal setup with some more unusual roles or an unusual mechanic.
Example setup: Pick Your Poison
High Theme. A setup that goes all out on Theminess but doesn't quite hit madness. A game with unusual roles and flavor, some complex mechanics,
Example setup: Haunted Village
Example setup: Greater Idea Mafia played with the Basic Two Scum Deck
Example setup: CultD3
High Bastard. A setup that is bastard and likely not in a fun way. A wild bastard dumpster fire. Still guaranteed to be playable. Death Miller setups fit here.
Example setup: Bastard++
The Abyss. A setup that is not guaranteed to be playable. Direct mod influence is possible. Might be something as ludicrous as Grand Idea Mafia, or something as sneaky as allowing non-players to directly influence the game. Mostly anything can happen.
Example setup: Deck of Astral Roles
Hadal Zone. Abandon hope, all ye who enter here. Definitely not playable. Think of trying to run Worst Idea Mafia and then altering the roles to be even more devious, and you'll scratch the 0 rating. Literally anything can and will happen.