I find that melodramas like to drag things out. In rom-coms, there are much more confrontational scenes. Melodramas seem to like to keep a drawn out secret that serves as a theme for the entire drama. That's risky if it's not a good theme, cause I just get tired of it.
This drama was pretty shaky. I sped watched the middle but I liked the ending. I think the characters all really started to shine again.

Mi Do - Shin Se Kyung
I haven't heard good things about this actress.
Her acting is appropriate to the scenario because she's depressed. And even if the actress isn't good, the character that she plays is written well. Mi Do is steely, a little volatile and she doesn't mess around. And definitely doesn't back down even if it gets her into trouble. I appreciated her resolve and she's not clueless either.
She's also not intimidated by the second female lead or the second male lead's forwardness.
She's a sad little thing and pretty much never happy which can be super annoying at times.

Tae Sang
Song Seung Heon is really excellent. His character is quite broody but he doesn't make it boring. The way he talks and his body language, he really owns the personality and the mood while still giving a lot of energy.
He handles Mi Do's pride with care. It's unusual to have such a kind chaebol. Tae Sang's character is fabulous until you get to the middle of the drama.
His gangster side does come up now and then. I liked how he is not a character that has it altogether. He is sincere and earnest and he tries so hard.

“Sorry that I'm stupid.”

He freely admits that he's never dated and that he doesn't know what to say. He's adorable. But he learns quickly. And Mi Do lets him know the rights and wrongs. I love him.

Friendship
The side characters are really strong. There are so many great brother relationships in this drama. The loyalty and the comradeship is A+. I like the trust and respect between the men. They are such mother hens to each other wanting to look after their hyung or their dongsaeng.

“You're my friend, my father, and my only family.”

The heroine also has a cute relationship with her brother. I love how much he admires her. He really thinks she's cool and awesome. And I like that she seeks him out when she's down because she knows she's safe with him and he can cheer her up.

Chang Hee
This guy is an awesome domestic goddess and such a great brother.

Jae Hee - “You sound like a grandmother.”
Chang Hee - “It's good to have a grandmother.”

Romance
What romance? This is so very screwed up.The drama should be called “When a Man's Obsessed”.

Tae Sang comes on way too strong.

First Half
Tae Sang and Mi Do have a really good dynamic. It's nice for a change that the girl is a little grumpy and unpredictable and that she likes physical affection. I like how real they feel because they go through their ups and downs and their feelings are all over the place. Their romance isn't clear cut at all. I liked the depiction of their uncertainty, their frustrations, and their struggles to make it work.

“Dad, let me date Han. I can dump him anytime if he's no good.”

I like that Mi Do takes charge of the relationship because he's so clueless. Han's lack of social graces is so endearing.
They have some beautiful cheeky moments together. There were times when I totally shipped the serious Mi Do and the sincere Han together. Other times, I completely felt the ill-fitting romance they were having. I can feel Mi Do's depression coming through and Han's frustration with her apathy. She takes his love for granted and acts like she's tolerating him. But on the flip side I liked her confidence in the romance.
I liked that the push and pull of the romance was a big part of the drama and that the tension surrounding it was a major anticipatory factor.

Jae Hee - Yeon Woo Jin
I was happy to see this actor again. He has a serious make out session. Probably the steamiest I've seen in Kdrama.

Music
I always appreciate a strings soundtrack.

Elders
I like it when there are different mothers because the drama feels less tropey, is that weird?