My anime rating system (will add fancy colors in the future Update Nov 11 '19: It's been over 4 years and still haven't done so. :):
10: A incredible watch. Definitely worth a rewatch.
9: This is certainly worth your time. Great show.
8: Very good, I recommend that you watch this.
7: A good watch, but it's for the best that it's watched only once.
6: It was alright. Not much to say.
4: Bad. Just bad.
1-3: I don't use these ratings ever. A 4 is as low as I go and I don't need to go further.