In the interest of fairness (and a bell curve), this is how I rate all dramas: 

Dramas I finished watching and would recommend to others: 7.5 - 10.0
Dramas I finished watching and wouldn't recommend to others: 5.0 - 7.5 (*)
Dramas I couldn't finish watching but may try again or seemed reasonable to recommend: 2.5 - 5.0
Dramas I couldn't finish watching and would definitely not recommend: 0 - 2.5 

All dramas that I've watched at least one episode of will get a rating (unless it was too long ago and I can't remember). 

This stops me from being partial towards actors I like and giving high ratings to dramas I couldn't even put myself through an entire series of. 

(* Exceptions are if my biases cause me to watch an entire series then have post-watch regret about the hours of life I lost, it might get a score less than 5)