I'll list some of my recent (last few months) dropped dramas here as the impression is still fresh.
I see already few people wrote that they dropped 'Another miss Oh'. I'm in, I also dropped it at the 1st ep. I didn't see any interesting story. Even if I admit that the story might get interesting in following episodes, I still wasn't interested in the actors and characters. Male lead's face seems creepy to me, the rest is just boring.
Beautiful Gong Shim. Main lead was funny there at first, but dramas sick, female leads weird I can't sympathize with her, plotline is uninteresting, too many of rich arrogant characters, all together feels like nonesense. I watched up to half of the dramas, skipping many scenes and even whole episodes, and dropped.
Same about 'Come back ajussi'.
Lucky Romance. The female lead is on top of my ban list, but I gave the drama a try. No, I really can't stand her face, acting, and her character is dumb and annoying as always. Dropped at 1st ep.
The Royal Gambler. Dropped after few minutes of the 1 st ep.
Entertainer. I could never watch a full episode, had to skip scenes and episodes and gave up. Actors and characters are ok, but the whole impression is boring.
Local Hero, My Little Baby. Both are just boring.
Six Flying Dragons, Mirror of the witch. - It's hard for me to get into a historical drama, I feel bored and tired watching them, even if cast is tempting...
Remember – War of the Son. Tired to see stupid policemen, corrupted jerks, stupid unpanished phsycho, always screwed face of Yoo Seung Ho, and the silly character of Park Min Young.
Goodbye Mr. Black. - Plotline is nonesense. Lee Jin Wook don't have to be an actor, let him be a runway and magazine model, he looks like an acting mannequin. Other actors did well but wasted they great skills on this useless script.
Sekai Ichi Muzukashii Koi. First 2-3 episodes it was exciting, but then there was no characters development, they seemed degraded. I losed interest and dropped.
Oh My Venus. Another bad realization of the idea of a fatty's transformation. Not funny but annoying drama. I dropped it at ep 1.
Madame Antoine. It could be much better, script lacks, don't like the female lead as well.
Battle of Changsha. Just not for me right now.