I can at least say that the times I've reviewed games, I look for more than what I do when just playing a game. It's happened that I've forfeited getting a free game to review over buying it myself and just playing it. Not because the "free" part taints what I'd say - it's the "review" part. Sitting, taking notes, being more critical instead of just playing.
The critical review angle works both ways - sometimes a bad game has good qualities worth mentioning and highlighting. Sometimes good games have really bad qualities. Playing a game as a whole, as many do, some of these things go amiss. I would expect that many user-reviews have that sort of take.
Truth is, there is no objective review - and everyone has different things they look for. For some it's the overall experience, for others its the sum of all the parts - and for others it's the greater context of what the game means or follows. Some people just go with what everyone else is saying because that's the safe bet.
A review is as valuable to the reader as he or she wants it to be. I've long held the view that people put too much weight into a score - it should be about the content. The pros and cons. The context. If it sounds like PR, then it's up to you to decide what value that has to you, if any. There is no lack of content about games, no lack of views, be it critics, other gamers, trailers, Twitch plays etc.
We're a smart bunch - I think looking at score aggregation is lazy decision making. If anything, it should be nothing more than a starting point.
(hence the OPs post). I know I wouldn't wait for all games to hit the bargain bin before buying them. There's a LOT of games I want to play before waiting years for them to end up on a sale. 