As we all know Steam is within the process of constructing a handful of small but significant changes to its Steam user review system whilst trying to perfect the accuracy of the review score each individual product has. In September, they implemented some tweaks that redesigned the client and the reasoning behind every review, furthermore the more endowed a customer is money wise, the higher the score that reflects its relevance.
With the upcoming changes, the review score (shown at the store pages and in various places throughout the shop from highest to lower ranked) cannot embody reviews that were written by those who have experienced a game through a free weekend, were gifted to them or have not paid for it. That kind of reviews will still be written, but they won't have the same value as those who have purchased it, hence it won’t count on the review score.
The system has been implemented recently, so it is going to take a few more days until the new update has utterly re-evaluate the scores, so the current scores are going to be constantly changing until the system has decided on its actual overall review score.
This solely affects pay to play games, so free to play games are going to keep their current rates unchanged. Meanwhile, Steam is going to monitor every change and gather every possible feedback, good or bad to improve itself.