Currently Online 
5 star system, with half stars. I picked that up long, long ago on Adventure Gamers, site dedicated to adventure games that's been around since mid 90s, since it gives broad tiers with half steps for some variance. So there definitions:
5 stars - Classic
An instant, hall of fame classic. Although not "perfect", we award our top score only to those games that set the highest standard for quality.
4.5 stars - Excellent
A superb game that excels in just about every area, held back only by one or two notable flaws or a collection of smaller ones that prevent the game from earning full marks.
4 stars - Very good
A game of very high quality. Although some aspects might have been executed better, we would recommend this game without hesitation.
3.5 stars - Good
A solid adventure that is generally enjoyable, though it lacks enough polish, consistency or ambition to recommend without caution.
3 stars - Decent
A qualified success; the positive aspects still outnumber the negative, but the weaknesses noticeably hinder the experience.
2.5 stars - Uneven
A near-equal balance of good and bad that can make a game either fall disappointingly short of its evident potential or be mildly entertaining despite its many failings.
2 stars - Underwhelming
There are some good elements that shine through occasionally, but generally the game is not a positive experience.
1.5 stars - Poor
Shows just enough promise to hold your attention, but is buried under too many problems to be enjoyable.
1 star - Awful
Offers a tiny glimpse of what might have been, but manages to execute just about everything wrong.
0.5 stars - Unplayable
A complete waste of time with no redeeming qualities whatsoever. We would not recommend this game to anyone, at any price. Avoid.
I do use X/10 with halfsteps as well for a bit finer steps, but 7/10 just doesn't feel as right to me as 3.5/5 stars.
Essay Pro