My Rating System:
5.0 = Indispensable classic
4.5 = Classic
4.0 = Minor classic
3.5 = Very good
3.0 = Good
2.5 = OK
2.0 = Mediocre
1.5 = Poor, but maybe a few good songs
1.0 = Bad, quite annoying
0.5 = Horrible, torturous shit

I try to rate with a scale that allows ample room for distinction in quality music. In other words, a 3.5 from me really is a very good rating. In my opinion, most albums belong in the 1.0-0.5 range, (as I think most albums released are pretty poor) and I don't want my scale to focus on the trash.

Albums in my collection which are listed as Mutiple, I have on both CD and Vinyl.

Also, I'm not trying to be objective and determine which albums are really the most important, most influential or anything like that. I'm generally just ranking my subjective favorites.