How much setting info is enough? And how much is too much?

Of course, this depends on the setting, the players, the characters and more. Horror often relies on ignorance, fantasy on discovery, acting like the Tenth Doctor on knowing it all.

Example: I saw the original short film of Mama (warning: creepy as heck) and imagined a completely different backstory than the one the feature-length version presents - I thought she was meant to be possessed rather than a ghost, that this was clearly a new development, and (due to the ending now chopped off) that it was part of a possession-based spin on a zombie apocalypse. Based on a very small amount of information, I went haring off in apparently a completely unintended direction.

I think a possession apocalypse is a pretty cool idea, but that’s by the by.