Appearance.... 
5 star ratings?.....
1 star......lowest 'quality' that warrants a rating.
3 stars...... average 'quality' competent but nothing special.
5 stars...... about as good as anything can get....you cannot imagine any way to improve it.
2 and 4 stars...... fit into the gaps as 'below average' and 'above average' respectively.
Personal prejudice/taste affects methodology.... unless you cna practise the idea of 'what would most people think of this' and let that also influence your personal taste/rating.
Most important thing is NOT to attempt to 'push' a rating in either direction by exaggerating it....eg you think 5 is not 'fair' that it should be a 7, so you rate it a '10'.
If you think for ANY criteria that it should be a '7' then rate it a '7'.
One reason for switching to 'stars' [and loaded rating ability matched to user level] is to disempower the 'drive-by' rating idiot who posts a '1' because he doesn't like purple or a '10' because the person is a mate.
