The descriptions for the boxes you can check when rating someone cover most of what you will encounter. However, I believe that there should be a box called "good sportsmanship" or "courteous". I think this is the opposite of "sore loser" and applicable when someone makes a mistake; especially in a team game. For instance, I made a big mistake in Game 5292785 which cost 2 teams the game, and I want to note that my teammate and the other team did not flame me for screwing up.
Specifics:
Add a box for the rating system.
This will improve the following aspects of the site:
