Cool Backstory Syndrome

[Anaraxes]

in a perfect world every campaign setting would have two books

Or one book if that's publishing reality, but divided into sections so that you can keep the spoiler stuff out of the players' section. If the campaign involves, say, the surprise appearance of hitherto-unknown dark elves, don't put rules for the dark elf race template in the player section, or have the captain of the guard in town described as "truly comes into his own during the fight against the dark elves".

Also, the players need flavor as well as the GM, not just crunch.