Concise description:
On player profiles, show the average number of players per game you've played
Specifics:
I've seen players who have won like 80% of their games. While impressive any way you slice it, it means a lot more to me if, on average, he's played against 4.6 opponents per game instead of 1.2 opponents. Perhaps you even build this into ranking also. So the opponents per game is a multiplier to your points, or something like that.
This will improve the following aspects of the site:
Will give users a better idea about someone's ability to win a game