Battle of Changsha and lady&liar are both Chinese so don't fit Korean recommendations.
Smile, you is one of my all-time favourite dramas so stick with it.
I've heard good things about Giant and Ojakyo bothers but I've not seen either.
A few long dramas I have watched and can recommend:
The best Lee soon shin - 55 episodes
Full house take 2 - 32 episodes
Five fingers - 30 episodes
Heard it through the grapevine - 30
Another two but not quite 30-
Bridal mask
Shining inheritancbithe 28 episodes