In my humble opinion, this is an average so-so drama. Not much of intriguing plots. Just a standard of boy meets girl – Girl meets boy – Hating each other first, then fell in love – Then another boy jumped in between to form a triangle conflict – Then a cancer disease and amnesia/Alzheimer inserted in as usual (It won’t be a Korean drama if absenting these two tear jerking factors). Pretty much standard stuffs.

Nana’s acting skill has improved a lot since I last viewed her in “Into The Ring” where she played the role of kinda lunatic girl - very energetic but naive in politic – Politic was a very boring subject to me so I didn’t enjoy that series much – Nana acted much more mature and feminine in this one rather jumped around all over, all day like in the “Ring”. The wardrobes clothes was superb, hairstyle was awesome and groovy - Excellence.
Lee Min-ki was cool and fit the role nicely. His role was similar to the “Because This Is My First Life” in which he played an eccentric landlord together with Jung So-min. By the way, it seemed they always gave him the eccentric’s role which he played best (Remember “The Beauty Inside” ?)

He was funny in his own way while forming up the chemistry towards Nana. His choice of clothes rather unique but still cool. I wish maybe next time he will change the hairstyle a little bit to show his whole face instead of this usual bird nest type.
Kang Min-hyuk (the third person) still having a lot of space to improve his acting. His role of a rich hot boy chaebol was dulled and shallow – Again, I put the blame on screen/script writer that carved him some very mediocre activities. In the love competition w/ Lee, even while he's having every advantages – Longtime friendship w/ Nana, young, handsome, rich, highly educated (from Paris), a cosmetic company CEO, he was still acting hesitantly and reluctantly.

The two secondary couples - Lee's male boss and Nana's female boss - Lee's male assistant and Nana's female assistant's - was even worse, trying to be funny in some unbearable overreacting ways, not even worth to mention.

The fantasy factor - The angel(?) guy that saved Lee from the car accident and warned him that he does not have long to live just added unnecessary confusion to the story.

This has reminded me of the 2008 Korean drama "Star's Lover" - with the 2 leads: Choi Ji-woo (remember her?) and Yoo Ji-tae.
Very similar story. The male guy Yoo was a poor writer and the girl Choi was an rich actress - But the acting and screenplay was far much better (again, this is only my opinion).
Choi-Ji-woo played an excellent superb role there. The role was an famous, air-headed actress. Think about it, an actress played the role af an actress - Choi was really, really "evil" - She used all of her stardom power, street smart (she grew up in an orphanage), thick-faced tricks, innocent-faced tricks, all kind of dirty tricks in luring, seducing the poor writer Yoo (Can you guess she succeed or not?).
She can kiss him passionately then instantly said that was only an act and coolly walked away. She can tell straight to the face to one rich guy who took the coat off for her that she does not wear other people clothes - Only then later acting freezing in front of writer Yoo to gladly received his jacket.
She told writer Yoo to drive her to a place (that she's been there a hundred times) with an almost sobering voice that she doesn't know the way there...
She demanded and entering his house (in kinda violently forced her way in), change clothes to his T shirt, ate his food, kicked him out to sleep on his bed, even using his tooth brush... and won't leave until she got what she wanted.
She acted and acted and acted... You wouldn't know where and when whether she was sincere or just acting.

Well, this is not the place to talk about another drama but please, you got to see it to enjoy the Winter Sonata legendary Choi Ji-woo acting skill.

This is only my humble opinion up to episode 12 of this series. Sorry if I offended anyone.