Nice question! I wanted to answer this hours ago when I saw it. This could get interesting and maybe we could learn from each other.
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I usually rate the whole drama after I watch it and I rate from the top down. I mean, everything's a ten and then I start deducting points based on two main categories: the story and the acting.
If you tell me a good story--well laid out and something that I could lose myself into, it's a 10. Usually I like resolved endings than open-ended ones--those can be frustrating especially when the writers makes you want it so bad but then they leave you in the air.
And second, there must be a good build up. A good story has development--I think Japanese dramas best portray this point. When they introduce a character, they usually do it casually and flash the new face on focus for a bit, make the new character and the protagonist talk or meet, briefly at first and then they focus at him or her at the next episode.
On acting -- Actors really play a crucial role in a drama because they give life to it--but they cannot do if their faces are half-dead or they just bear the same kind of expression for ALL feelings. :\
Also, there has to be character development. The supporting cast is there for a reason. And if a drama incorporates its characters for the enhancement of its story, no matter how small or big their roles maybe, it's a 10 for me.
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I've recently tried averaging a drama's overall rating from the episode ratings with the same guides above. ^_^ They're helpful but when you rate the whole drama, and weigh whether the things that I dislike about it are merit enough to deduct a point or not. I try asking: Was the acting was really bothersome that it affected the mood? And the female lead needs to leave him because...? What's the story's point? Do I agree with that? And so on... :D
