First of all I would like to say that I liked the cast especially the main leads. They had good chemistry and their relationship was sweet. They have good acting skills as well, especially the male lead.

Now lets get to all the problems.

Honestly speaking I personally think all the blame for the problems in this show goes to the writing. They had a pretty good premise which they ruined -No, sorry, BUTCHERED - time and time again throughout the show.
I feel as though the director didn't do a good job either. There is no consistency in the plotline and characters.

Lets start from the beginning itself the logic is thrown out the window by all characters. Even though most of these characters are considered smart but we almost never see it. First and foremost why doesn't the doctor say her that she wasn't hit by a car considering she has no injury that might reflect this belief of hers. If it is a hit and run then why aren't the police involved? She remembers seeing him but doesn't remember not being hit by a car.
There was a lack of consistency when it came to the second leads feelings. One second he talks about how cute she is and the next second he doesn't seem to even care about the fact that his friend is dating her.
Another flaw in storytelling was that the main female leads feelings for male lead came out of nowhere. Actually the main female leads feelings were all over the place and a total mess. One moment it feels like she is falling for the second lead, although she carries another guys photo in her book. She gets over the Tang Yu guy just because he insulted her college, this is weird considering the fact that she apparently liked him since high school. She accuses her father for not being her biological father and he does nothing about. Shouldn't he be angry or offended that somebody was defaming his wife?
Lets talk about the main male lead now. Throughout the show he throws money around to solve all the problems. Until the 35th episode he is sweet, kind and generous, although she misunderstands him time and time again, but in the 36th episode he loses his memories and apparently his personality as well, which make no sense because the second lead says repeatedly that the male lead is sweet and generous. the male lead is shown as somebody who is smart and logical but he doesn't try to do a DNA test and/or ask his father the truth (I know his mother asked him not to, but it still makes no sense), instead decides to break up with her just because there is tiny bit chance that she might be his sister.
The later half of the show has no specific storyline and is all over the place. One second we are told they might be siblings and their pain is poorly executed and barely shown. Then there is He Mei, whose involvement is for dramatic purposes but also shown very poorly. We are told about maturity and growth in characters but we never really see it.

So for all these I would have to put the blame on SHODDY WRITING JOB.