Ever since its inception Valve has constantly been tweaking and upgrading the Steam user review system. Back in May they released perhaps the most important change so far, the ability for new reviews to rise to the top rather than forever remain at rock bottom, and soon they will be doing another major update.
Long story short, once this update arrives the review score will no longer include reviews by users that received the game for free, such as via gifts, or during free weekends. These users can still write reviews and have them rise to the very top, but their review will not count towards the overall score. Obviously, this new system will not apply to free-to-play games given their unique position.
While I can certainly see the logic behind this move I don't think its going to be nearly as impactful as some of the other changes Valve could implement. For example, almost every popular game is infested with abysmal reviews that all boil down to a single catchprase. Since they are easy to read and digest they tend to rise to the very top and clog up the whole review section while adding absolutely nothing of value. Getting rid of these 'reviews', or at least giving the community an option to combat them, would go a long way towards making the Steam user reviews more pleasant to browse through. I'm aware its not an easy problem to figure out, but it is one that Valve will need to eventually tackle.
To return to the topic at hand, I must admit I'm curious to see how the review scores for Early Access games will shift once all of the 'freebies' go out of the system. Or better yet, what will happen with games that got a massive surge of reviews during recent their various free weekends? Whatever the case may be, we'll find out soon enough as this system is currently in the process of being rolled out.