My rating system is as follows:

5 points for each song (by .5s)
15 points for musical content including actual vocals (taking into consideration the type of music and the intent of the artist, i.e. I would not hold lo-fi folk to the same standard as more complex music of a higher production quality)
15 points for lyrical content (keeping in mind its relationship to the music. For instance, I would hold lyrics to a much lower standard than poetry, if it is powerful combined with the music)
10 points for cohesion of the album
10 points for originality, influence, experimentation, etc.