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1-5 is the best, because:
1: bad
2: below average
3: average
4: above average
5: great
3 is halfway and reserved for average games. Above average, that is, good, games get 4 but are still below 5, which is reserved for very good games. Then there's 2 for games that might be playable but are below average and 1 for games that should be avoided. Make it 1-10 and you'll have 9-10 for great, depending a lot on the reviewer, 7-8 for above average, 5-7 for average, and anything below is just bad, 1-2 being there just for the worst games that are reviewed because the reviews might be funny. And make it 0-100 and it'll be a lot like 0-10 with the exception that you won't necessarily be able to properly explain differences less than 5 points.
Seriously, 1-5 is easily enough to see if the game is good and if you want to know more details, you should read the review anyway no matter the scale. Only a fool trusts a game whose metascore is 92 to be clearly better than a game whose metascore is 90. And I'm not sure we even need seperate scores for games above 95 - they're all supposedly some of the best games ever.
