I like a movie-style 4 star system with the following distinctions, usually these are what SHOULD classify a drop, or raise in numbers. Now very little would fit ALL of these categories in any one rating, but I think these are good classifiers overall, and they should encourage people to read the review to see where the game hits within this criteria, I found MANY reviews make a lot more sense if you actually read the text as opposed to simply looking at the score.
4 - Universal Appeal, Plenty of Artistic and Mainstream merit, High Fun Factor, Long Playtime or Lots of Replayability.
3 - Wide Appeal, Either Artistic or Mainstream Merit, Good Fun Factor, Worth Playing at least Once.
2 - Narrow Appeal, Merits are very selective, its fun but can be either taxing/frustrating, short/no replay value/too long.
1 - For Fans Only, Merits based on dropping your standards, fun is limited, short with no replay value.
0 - Postal Series.
or to make it easier...
4 - Buy It unless you KNOW you will hate it.
3 - Think about it, read the review, then buy it.
2 - Rent it first, you may have misgivings.
1 - Think about it, read the review, rent it, then, if you still love it, buy it.
0 - Games like this are bad for you, me and the games industry.