I love most if the main actor/actress really can act with variety of expression especially if i can feel their tension&chemistry. I need their main character/couple fill the story 70% or 80% of the complete episode. I got confused with too many side character I'll even forget the lead name. I don't have big problem with voice dubbing but bad CG is a No No for me. Repetitive & predictive scene is normal for any drama. It's kind of annoying but how they film it & actors acting will decide for me to say yes or no. Hit or Miss. For me, the only drama that actors acting save the whole weak production is Guardian (pardon poor english, i wish i can elaborate more but my grammar is limited)
I just watch her in Knowing Brother in netflix & i remember seeing her in Over the Rainbow. I know she's a good actress mostly in dark movies but haven't seen her movies yet. She's my age & seeing her in KB, now i respect her more & will watch her work because i love strong hardworking woman especially when they truly learn martial art. Most action drama/movie are dominate by male character. I hope it would change since there's more & more actress is diving into the world of martial art
Oh, i did not know this is for 2nd season. I'm about to put a comment about the 1st one. Good story btw. Looking forward to their subtle cat&dog communication. It was fun.
Kim Nam Gil also frequently does action.And JCW said he had a bad experience with the PD & Writer of K2 adding…
I do remember jcw say k2 will be his last action genre. Kng does do action sometimes but i don't have the impression that he love martial art. Korean artist usually show they do gym&boxing but not anything else. I'm looking forward to byunyohan into more action
Only few senior actor that willing to go on with action drama all the time but they have to love martial art very much. One that i notice is leejoonki & janghyuk. Jichangwook unfortunately have stop doing action genre
K-Drama 
(pardon poor english, i wish i can elaborate more but my grammar is limited)