Well, my rating method is very simple. It isn't a cientific or a professional method. It is only a simple way of a humble guy like me show his opinion about game. A gamer that play just for fun. And games are made for fun.
Basically I consider if the game is fun. If it makes me play without stopping, whithout getting sick of it making me play another game on its place, in other words, if the game is addictive. I check if the story is good or not. Check its jogability. The game can't be too easy nor impossible. And that's it.
I do not take account of graphics. I analyse if the game has enough to make me have lots of fun at the time I played it. So I can give 10 to a game very old, that has marked my life at the time it was released.
Yes, just be prepared 'coz I gonna give lotta high rates here. But it is all reflection of the great time that I spent playing it, recently or in the past. If you have the same taste as me, well, doesn't think twice in playing games that have 8.0+