Hwang Jung Eum- her face expressions, her voice (she should not really do narrations, it sounds like she's reading off from a script), and her inability to have romantic chemistry with her male leads.
Park Shin Hye- I've seen her since stairway to heaven, thought she was good. But her popularity grew faster than her acting skill.
Lee Min Ho- I don't know, maybe it was because his popularity is so big yet I find nothing special about his acting.
Lee Jong Suk- He seem to act like himself, and I don't really like that. All his characters seemed like one person with the same attitude and mannerism. I find myself not wanting to see him in a drama that I'm anticipating for, but the roles seem to always go to him like Pinocchio, W, Doctor Stranger, and While I was Sleeping.
Yoo Ah In: good actor. It's just my opinion that when I see him in a role, I imagine someone else that could have matched the character. I think it's his face and build.
others: Jang Geun Suk, Nam Goong Min, Yoon Eun Hye