Numerical or Percental Scores in Games are for idiots who are unable to form an impression based on opinions presented to them.
You can not apply a numerical value to something like a game, wich may not be the sum of it's individual parts. Same with Music or Movies. Yet everyone tries.
"The Walking Dead" (Adventure) for example, on pure Gameplay terms, is at best mediocre, and the shooting and sneaking is basically worse than in "The Walking Dead: Survival Instinct". Yet it's writing and it's presentation merit a higher rating. There is no way to give an objective numerical rating, no matter how you try to approach it, you pull a meaningless number out of your ass.
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As for actual written reviews...
Critics tend to play more games, as in a lot more, and most importantly, they tend to play the best games and the games that are so awful that no gamer in this community would even touch them just "for fun". With that in mind, plus their subjective opinion, plus their personal preferences, plus their (hopefully) sense of journalistic integrity that prohibits them from endlessly bitching about games they don't like or grown tired of (after all, say what you will, on an objective level there hasn't been a really bad Call of Duty Game for a long time, regardless on how tired and repetitive the games seem in the larger context), its obvious that they view games differently than a guy who plays 2 or 5 or 10 or 20 or 50 games a year and pays hard cash for it.