I think a possible way to reduce the number of crap ratings is to have an option to tag your mission with one or more of the following tags: "combat", "diplomacy", "puzzle", etc. This could be a new type of search filter, which would make it easier for people to find the kind of missions they want, which would reduce the "not enough combat" or "crappy story" reviews we all hate.
"It's not safe out here. It's wondrous, with treasures to satiate desires both subtle and gross. But it's not for the timid."