Kind of cheesy in some ways but I really enjoyed The Masked Lover.
Also Someone Like You
MARS - a classic, old but gold!
A Good Wife - liked this one because of its mature protagonists & how it cast a critical eye on the unreasonable expectations Asian societies place on everyone - parents, children, lovers etc. More slice of life, but it had an okay love story going on in there too.
Also I was about to recommend C-drama Too Late To Say I Love You, but I see you have it marked as 'completed' on your list, yet no rating? Why?
This drama features one of THE most romantic and passionate romances there is! While the plot entered into frustrating, convoluted territory a lot of times, I loved the romance because it was so mature, between two grown of around the same age. I'm so tired of the usual silly, innocent so-called 'pure' (eyeroll) romance between 20 somethings in Kdramas ... and noona romances, which it seem like if a k-drama isn't a stupid cliche romance between 20 somethings, then it's a noona romance. Which, in general, I don't actually mind, but I get fed up real quick when it seems like we're being forced fed an agenda. And the hypocrisy of MDL users when it's a noona romance vs a romance between a younger woman/older man. I mean, men have gotten away with a lot throughout history ... but I still find this hypocrisy annoying. Ok, totally went off on a tangent there ... lol