I really don't have much of an issue with a 50 or 60, as they mean average and above average. If a game isn't really striving to break boundaries in terms of gameplay or graphics, some people who aren't into that type of game will find it average or slightly above. No, my problem comes from reviewers rating a perfectly average/above average game, without many or any glitches/bugs, below average just because it was a hyped game. Some even trying to make a statement and rating it a 10 or 20, usually reserved for poor looking games that are barely playable because of poor game mechanics and/or glitches and bugs.
Take your Uncharted 4 example. They rated it a 4, or below average, when really there is no way an objective reviewer can rate it any lower than 6. There is absolutely nothing about that game that is below average. Maybe the game isn't for you and you think the gameplay is average, but as a reviewer it is impossible for you to ignore the graphical and technical achievements of the game. The graphical prowess, and the fact that the game has little to no glitches/bugs warrants it being bumped up a notch or two.
And really, I get annoyed when things go the other way, as well. I see too many games that are a buggy mess or just look average in terms of graphics getting 90s and 100s. It's fine to love the game and its story/characters/gameplay enough to enjoy the game, but that is no excuse for a reviewer to no take off a notch or two for those problems. And who says you can't like games in the 70s and 80s? Many people do. In this case, I think the problem is two-fold. One, they are worried about companies not providing them with free copies of games if they continue to not hand out 90s and 100s. And two, they don't want the hassle of 100s/1000s of fanboys coming in and complaining that their latest BIG exclusive only got a 70 or 80, when "it totally deserved 100."