Valve just recently introduced a new feature for its game reviews on Steam called Histograms. In Steam Histograms you are able to see the history of the reviews based on selected time frame.

This feature was introduced because players “abused” the review feature for example where they put negative reviews on Dota2 game and blamed it for canceling Half Life 3 game.

Example of Steam Histograms on Dota 2 below with High Volume of Negative reviews detected.

Steam Histogram example