Hello there :)
My ratings strictly depend on the quality of the drama and are never based on whether I love the actors/ship or not. I just skip the content and shows I know won't be my type. That's why there aren't many shows I have rated very low. I simply just don't watch what I cannot like. Ofcourse good plot, good chemistry and good development hook me up fast but I'm not very patient in general so if I actually start a show and the chemistry sucks, plot is a snoozefest or problematic/cringe crap is going on I drop it.
Here's how I rate my shows:
10- Masterpiece! No notes. Perfect from start to finish.
9-9.5 - Amazing! Maybe some parts are dragged or maybe I was just not in a mood to give it a perfect 10. But just as good as a 10.
8-8.5 - Pretty good. Has flaws that I couldn't ignore or plot points that left me unsatisfied but is still overall a good watch.
7-7.5 - Watchable to me. Might be partly boring, dragged out or has plot holes or nothing much to offer other than good chemistry but could still finish.
6-6.5 - Forced myself to finish the show, it could be because of bad plot/ bad characterization/problematic track.
5 or below - Either trash plot, trash chemistry or trash direction. Disliked it!