Hmmm, I truly don't think I have ever regretted a drama. I feel that its good to have that experience of disliking a story or drama, otherwise how would you know how much you would hate it or what types of things you don't like happening in a drama.
A drama can't be completely perfect. Even my favorites aren't perfect. But you have to have various types of dramas to know that. So I don't even it as a loss of time.
I have read a book that I ABSOLUTELY HATED, I finished it simply so I could see how the author wrapped it up. My hate for the novel was so great, I seriously forgot the title of it XD