User blog comment:The Milkman/Multiplayer Ideas/@comment-1503545-20120428205353/@comment-4237253-20120428210041

That would be a fun way to improve playability. Games like U3 and CoD have these kinds of challenges to give you something to work towards. It's the same idea that applies to achievements/trophies. Give us a goal, and every kill feels more satisfying, because we are contributing to a goal.