This is my rating system:

10: ultra top league - almost perfect

9.5: could have made my ultra top league but have some noticeable imperfection

9: excellent, top league but not among the ultra top

8.5: very good but not outstanding

8: generally good but not quite there yet, or excellent with some major/glaring flaws.

7 - 7.5: some good parts.

6.5 or less: don't waste time.

I am very selective with dramas I watched.  So typically most of my ratings are 8 or better.