King Geunchogo is a historical drama, and Eunjung and Qri should be honored to even be in it, as idols usually aren't in them due to a lack of talent. Eunjung proved herself in Coffee House and won over viewers in Dream High as being the only idol who could act. Suzy almost bombed that drama, and IU's cuteness overshadowed the lack of acting she was required to do. Taecyeon was ok and Wooyoung's character was one dimensional, so he can't be fairly judged.
On the other hand, Qri is the second best actor in the group. Eat it Jiyeon fans. Whine, bitch, whatever, but it's the damn truth. Go watch Spy Trader Kim Chul Soo. It's a one episode drama special and Qri's acting in that 60 minutes was better than what Jiyeon has done to this point. Qri may one of the least popular members, has no vocal talent, can dance somewhat, but a) she cures erectile dysfunction and b) she has the potential to be a good idol actor. She's actually getting a chance and a roll that will last for more than two episodes.
I've seen the first four episodes of King Geunchogo and it's good, but historical Korean flies over my head like logic flies over the head of fangirls, so it's tough watching them. But it is a quality drama from what I've seen, and I'll probably watch it during the summer.