This is how things should work: higher-rated games will get better sales than lower-rated ones. And while there are plenty of outliers, Ars Technica's Kyle Orland discovered that yes, for the most part, higher-rated games tend to get better sales.
By compiling data released on Steam, Orland discovered that getting a 90+ Metacritic score almost guarantees some success, with games selling at least 50,000 copies when reaching that score.
By aggregating games together into 10-point Metacritic score ranges, Orland discovered that games that score 90+ will sell nearly 800,000 copies on average. Games that score between 80-90 will sell about 250,000 copies. That's a tremendous difference, which only further emphasizes why it's so important for publishers and developers to earn high scores.
Games that score between 40 and 70 can expect sales around 50,000, proving that at a certain point, the scale doesn't really impact purchases. The rare game that gets below a 30 will end up with fewer than 10,000 sales on average, showing that low scores may dissuade purchases as well. (Shacknews' average Metacritic score is 65.)
For the full report, visit Ars Technica.