Courtesy of critic Robert Christgau, here's how to rate rock albums of the 70s:
http://www.robertchristgau.com/xg/bk-cg70/grades.php

"A D+ is an appalling piece of pimpwork or a thoroughly botched token of sincerity." etc.

Christgau has since upgraded his rating system:
http://www.robertchristgau.com/xg/bk-cg90/grades-90s.php

"An A+ is a record of sustained beauty, power, insight, groove, and/or googlefritz that has invited and repaid repeated listenings in the daily life of someone with 500 other CDs to get to."

I demand that the word "googlefritz" be included in at least one review in the next issue of The Word.