I'm not sure my contribution here will be of any value. If I watch something that I consider worth a 3 or less, I'd rather drop it than stand the torture. I usually don't rate dramas I drop, unless I have struggled somehow at least to the half. So my list includes only:
Romantic Princess (TwDrama) - The acting is ridiculous - I let it pass. The music is horrific - I closed one ear. The scenery is impossibly unrealistic - I smiled. The plot started a little cliche but I was willing to see where it would lead me. Then everything became convoluted, repetitive and, if possible, the acting worsen instead of improving, as if they were all late for the last flight and had to rush like mad. Not even the pretty face of Wu Chun could save the day. :P
Yamato Nadeshiko Shichi Henge - I didn't like anything about it. Not the supposed message it sent, not the acting (and I'm a huge fan of Kame), not the repetitive scheme of each episode, not the characters and their silly antics. Why bother?