Valve is still in the process of tweaking the Steam review score system and there’s another change being made.
Following changes made last September, user review scores will now not be counted if the user received the game for free. This includes gifted games, games played over a free weekend, or any other kind of freebie. Reviews can still be posted, they just won’t count toward the overall score.
The changes are being made right now and should be complete in a few days as scores are recalculated. The new rule obviously does not apply to free to play games.
Valve explained by the change is being made adding, “We’re continuing with a few more changes in this direction to improve the relevance of the score by better reflecting the sentiment expressed by invested, paying customers.”