I've seen many bad reviews about this drama and it actually depends person to person. This is my point of view to this drama.
•This is like really really slow paced drama(so if you don't like slow paced drama don't watch it) but somehow I think that made me a character of the story, I was feeling the story actually (even if it's boring with no plot twist)
•So basically the boss (after a unlucky/terrible event which was kind of stupid but let's ignore that) had trauma which made it hard for him to talk to anyone, even with his parents, this is when main female lead comes to seek revenge but ends up having feelings for the boss,so she starts to try and understand the boss and wants to change his personality( which was like abuse to everyone, which in way it was, but it isn't). When both discover they've feeling for each other, things take turn and truth clears up and the trauma heals that's it, that's the story.
• The problem with this drama is writer should instead calling the boss introvert should've mentioned (after the unlucky event) has shy personality disorder (which I noticed after watching the drama) but I think maybe the writers simplified it to "introvert" to make it simple for viewers.
•And now to people who think the female lead was abusive and stuff, let me tell you people with shy personality disorder needs more than whatever female lead had done to make him normal, this is the reason why I think she was right in her way. After she actually understood( in 14-15ep) what boss was really like(an introvert) she gave him his space and respected him. Again there was no where written or directly shown in drama or anywhere that the female lead is extrovert (and she is not btw) so stop making assumptions, she is just a little more carefree, laid back than the boss is. However that doesn't affect their chemistry in any way. It's beautiful believe me.
• The unlucky event which happened was baseless but I think she(the deceased secretary of the boss and also female lead's sister) took a big step for what happened even if it was out of guilt, she should've talked it out nothing of this would've happened, but I get it must be hard to talk about what happened with her (everything related to her crush's family). And yes Mr. Kang is a very bad human being (you'll get to know why if you watch the drama )
• It'll be confusing with how the director put forward the scenes, it'll not make sense at all if you watch it with breaks so you've to watch it all at onces, again if you want to, even if there is no plot twist it's simplicity is what makes it different ( at some point it'll get boring but if you want to finish it you can watch it). I think the intention of the creator was to make introverts believe that being an introvert is not something to be shameful of and wasn't to offend any introverts by drama scenes. As an introvert I did relate to the story(and it'll depend person to person).
To the people after watching drama think people who watches this drama and likes it is high on something or mad I'll just say this politely just because it isn't something you like doesn't really mean others have to hate it too. Others can like it and that is okay you can hate it and that's okay too but just don't use words like that...
After reading my comment if you think it's a type of drama which matches your likings then please do watch it, it's an amazingly simple drama which I do like.