Aside from trusted individuals or word of mouth, reviews are the go-to thing for getting a general idea of how well a game has performed under the scrutiny of a single reviewer, who may or may not provide a favorable overview of the game in question, or provide anything outside their own relative experience.
Because video game reviewers are limited to only what they know, reviews for a given game can vary between those who review it; someone with limited review experience may only review a given game based on their experiences with the game alone, and someone with a lot of review experience my review a game based on their experiences plus reference it to other experiences in other similar games, and provide comparison and critique where applicable. Please take in mind that someone with limited review experience can also do this, too.
So, as reviewers are limited to what they know, it begs the question of whether or not we should actually pay attention to reviews (especially reviews that provide associated numbers), because each review is typically written up by an individual, whose experience and practical knowledge are what can condone or condemn a game; a single person can dissuade or persuade others to buy a game based on their own experience and influence.
It’s quite a palpable responsibility, as a reviewer with a wide sphere of influence can result in a game losing a lot of sales because of their opinion of said game, if they consider the game in question to not be all that good. The other side of the coin is also true.
What’s even more insidious is that reviewers can be accused of their opinions “being bought” if they give a game a favorable review, even if the review itself is based off of the reviewer’s experience alone, but I digress.
Since each reviewer speaks from their own perspective, with all the practical knowledge and experience they have at their disposal (or lack thereof), a review of a game is essentially the opinion of an individual, whose words have the potential to influences hundreds of thousands of people.
Numbers provided by the reviewer only perpetuate this, as people can just glimpse at the score and make their decision based on that alone. What’s more is that a given score a game can b e the exact same score as given by a different reviewer, but for completely different reasons. Because there is no definitively uniform method of reviewing games (at least to my knowledge), there’s no way of knowing which review is the “right” one, if there is actually ever a right review.
Websites like Metacritic work around this problem by averaging out hundreds of reviews between critics and amateurs alike to amount to appropriate scores, but even then a game can be brought down by those who are inexperienced at reviewing games properly and so give a game an unnecessarily low score based on their own experience (which can be anywhere between minutes or hours of logged gameplay).
Reviews have always been a muddy subject with me, because the opinion of an individual can be considered the final word on a game, and can be subjected to heavy debate by those who do not agree with the reviewer, seemingly forgetting that the review itself is based on the reviewer's own experiences, which--despite how objective they might be--are subjective in of themselves.
Which is why it would be good advice to take each and every review of a given game with as much salt as you’re willing to pinch, as you’d essentially be reading a single individual’s perspective regarding the game in question, whose own experiences and knowledge may differ from that of others.
At the end of the day, the arbitrary number slapped on at the end of a review is almost entirely based on the reviewer’s opinion; a single person can rate the same game anywhere between zero and 10. As there’s probably millions of reviews out there on all sorts of games, paying attention to their associated scores can be unreliable and inconsistent. Having said that, you’ll usually find that professionally review scores from multiple outlets tend to give a given game the same score, whilst a score from amateurs can be all of the place.
What I’m saying is this: you shouldn’t take an individual's word on a game’s given score, unless you trust that word. Read as many reviews as you're willing to, and make an informed decision based on that.