It started really well, I was really invested in the beginning. The revenge plot, the romance that's so close yet so far, an impressive girl to pursue the guy, and the interesting side characters, really gripped my attention in the beginning.
However, after a while, Sae Royi and Oh Soo's romance started becoming stagnant, did not move forward at all, the character of Yi Seo in the beginning was cool and independent, but she just became needy and selfish later (although on a side note, she gets the guy so maybe we should aspire to be like her, lol).
What I hated the most was romance part, Sae Royi and Yi Seo didn't even make sense (every boss might as well start marrying their efficient secretaries) . Being grateful and falling in love are very different things but this movie blurred the lines between that. This was the breaking point for me. It might sound silly but to me romance in a story is of importance, not as high as the plot (which was interesting in the beginning but towards the end, I started losing interest) itself but without an attention-grabbing love story, and a lethargic plot, I just decided to drop it but not before watching the last scene so I'd know how it ended.
Not rewatching it, but I loved Park Seo Jun (I firmly believe the character he played was at fault, not the actor)
P. S. You could try watching and form your own opinions, mine might've been a bit biased coz I don't like stories where a new girl succeeds in breaking apart an already established couple.