Pretty much all of your criteria are met in:
- Time between Dog and Wolf: I know, it's old, but it's very, very good. Trust me, at least watch a couple of episodes.
- City Hunter: I love almost everything about this drama. I even prefer it over Healer, but that's a matter of opinion. Strong female lead, double identities, loads of action and drama, you name it....
- Yong Pal: Starts out as action/medical, then turns more into a revenge drama. I loved it, though.
A bit less action and more mystery, but also great:
- I remember you/Hello Monster: The romance is much slower in this one, but they share a special connection. Fantastic drama.
- I hear your voice: Noona romance; mystery/law but also a bit action.