After a recent round of changes to the review system to fight "review bombing", Steam has detailed further changes coming as a result of manipulation by "a small set of users on the far extreme that are clearly trying to accomplish something quite different from normal players". In short, small groups of Steam users are marking reviews as "helpful" to push either all negative or all positive reviews to the top of the default reviews shown. As a result, this can find viewers seeing an overabundance of negative reviews for games that are still considered "Mostly Positive".
Of the 11 million people that have used the helpful buttons, most follow a reasonable pattern of usage: Typical players rate a few reviews as helpful or unhelpful while deciding whether to make a purchase. However, we found a small set of users on the far extreme that are clearly trying to accomplish something quite different from normal players, and are rating more than 10,000 reviews as helpful or unhelpful on a single game. This behavior is not only humanly impossible, but definitely not a thoughtful indication of how 'helpful' each of those reviews were.
Because of how many reviews these users are rating, they each have a disproportionate amount of influence over the display of helpful reviews and cause certain reviews to appear more prominently than they should be.
As a result of the above, Valve has detailed a pair of changes coming. First, there will be a new calculation applied to the "helpfulness" of each review that will further determine if the account is trying to manipulate the system. It is specifically targeted at those "that are far outside the norm".
Secondly, positive and negative reviews shown by default will be displayed in an approximate proportion to the game's general review score. "For example, if the game is reviewed positively by 80% of reviewers, then the ten reviews shown by default on the store page will be 80% positive, showing eight positive and two negative."
You can read the full blog on the Steam blog.
