Yes, I think that Secret does a good job of showing change in character. First, the male lead hates the female lead (
in here, he actually has a good reason...it's because she lied and said that she killed and left his gf for dead in a hit and run accident), but since he's intelligent, he starts to find out the truth and get to know her so his feelings for her change over time. This is a really sad drama but it's got a happy ending.
Kdrama is really popular where I live too and this started a few years back but I avoided it for the most part because a lot of them have such sad endings.
But nowadays, I check out the ending first and normally I go for dramas with sad parts...but they have to end happily or else I don't watch lol. In Secret, I feel so sorry for the girl but the actress is good. So is the actor playing male lead. I think they won awards or something.
Anyway, I'm still curious to see how SSK will end but I wish they wrote it so that the p'ek wasn't evil. If I had written it, I'd make all the scenes willing and I'd write it so that the male lead changes in the middle of the series for the better. I would also remove all the other couples (except for maybe Lydia and Kan) because it's way too crowded.
I really like Tawan and Duen's sister relationship though, that's one thing I like in SSK because not many dramas I've seen focus on sisters.