Campbell
Relaxed Intensity
My answer on this is it depends. Compelling prose that makes me want to invest in the game's setting is crucial, but it does not have to be long (although it can be). What I'm not really a fan of is text that combines lore and game rules in a way that makes it hard to tell when one starts and the other begins. Despite being one of my very favorite games Exalted Third Edition is terrible about this. So is Vampire the Requiem.