It would be great if we could contest ratings that are either unfair, unhelpful or spiteful.
Also, ratings without feedback are not constructive. A secondary suggestion would be to make it impossible to give a rating without giving feedback on why it warrants 1, 2 or 3 stars so that the author could learn from their mistakes.
Going back to the first, the ability contest ratings and reviews that reflect more upon the reviewer (ie reviews that say the mission is awful because they can't find the location when it is clearly listed in the description/intro text) than the reviewed would be nice so that unwarranted 1 star reviews could be invalidated.
However, if there is already a way to contest ratings, I would be interested in learning how. I saw no obvious way to do so.