I really went back and forth watching this one. The first couple episode are very slow to start and I struggled to hang on. The comedy is a bit of hit or miss for me and the general tone of the show is a bit of a whiplash of 4th wall breaking camera spiking from the two main leads, to murder and corporate espionage.

Someone in the comments here said it's like this show is a big puzzle with pieces that don't fit well and I have to agree with that. The show likes to throw twists and turns without fully fleshing out concepts or just concluding them by adding a new twist. That's not to say the story is entirely bad. The moment to moment writing is pretty satisfying and the delivery of the story was fairly fun to watch, especially up to episode 12 or so.
However the constant tone shifts throughout the show and scattered main plot make for a confusing watch. That's not to say you'll be left wondering what happened after watching the show but you'll be asking why the writers gave such odd motivations for the antagonists. The explanations on the last few episodes were pretty unsatisfying for me and left me wondering what the show would've looked like if it focused on other parts of the story inside. The premise set up after the first few episodes seemed like such a fun idea and had so many great places where they could've taken the show; but instead they keep developing and pushing too far, leaving behind the best ideas of the show behind.

When it comes to the acting, Krystal and Kim Jae Wook are super strong leads for a romcom like this, regardless of how I feel about the story. Krystal plays the overworked and underappreciated secretary very well and her charm is here in spades. She sells the character well and both her comedic and emotional moments are felt throughout.
Her character's writing fails her in the latter third of the show though and she falls into the same trope of the female lead that most kdramas end up going. She goes from being a capable, funny and impassioned lead character to being a passive supportive character to the male lead while the main plot of the story unfolds around the male lead.
Kim Jae Wook does well in the male lead role too. Just like his performance in Her Private Life, he is great at playing the cold tsundere CEO. I think just as a male lead actor should, he conveys his sensitive side of the male lead character just as well as his capable businessman side.
I do like that this show isn't interested in a second lead syndrome and in terms of the romance parts of the show, it focuses on the two leads. However the side characters in this show are nothing to write home about sadly. No acting here is too over the top (other than Im Won Hee but he's so typecast, it's hard to blame him.) and everyone plays their roles fairly well.

I think if you can accept how the plot unfolds you'll really enjoy this drama since the pieces are all there. For me it fell completely flat though and without the acting of the two main leads (and honestly too much free time for me) I would've dropped this show before it's conclusion.