Most grading scales are waaay too complicated. Here's how I grade my CDs. I only grade the discs, NOT the case or artwork. 

Excellent: Almost new, not a sealed package. 

Very Good: A few light scratches, but plays perfectly.

Good: Light scratches, but more than a few. They are noticeable, but do not affect playback.

Acceptable: Quite a bit of scratches, but disc still plays. May have some deeper scratches. May not work in all CD players.