I usually just go with 'Out of 10' in about 99% of cases, and I don't mind decimals (7.5, 9.5, etc).
However, in some specific cases I prefer to talk about select titles in terms of 'importance' or, when it's a Masterpiece, with pure respect beyond merely giving them a scoring system. They would be my Hall of Fame games, my Masterpieces, where even a "10 out of 10" isn't properly descriptive of my appreciation and gratitude for what they brought to and meant for me. I don't 'rate' on a scale when the art of a game (under any form within it) solicit an emotional response or reaction. But all of this happens extremely rarely. In the hundreds upon hundreds of video games I've played, I don't think I could count more than maybe a dozen like this.