This series is definitely for a more mature audience, now I get the 19+ rating. It's not your typical fluffy rom-com with a lighthearted tone, sweet more caricatural than real characters and heart fluttering moments.

Well, this series does make your heart flutter, but for other reasons, namely, a) the sexual tension between the leads and b) the anxiety and unease that comes along with it. It initially is a realistic depiction of what dating nowadays looks like, of trust issues, fear of commitment, the struggle to really open up and the stress when you can't read your crushes' mind and intentions. When to call yourselves exclusive? Is there even such a thing? Nowadays, is there really the option of falling in love and staying in a monogamous relationship when there might always be 'a better option' out there? You might be one swipe away from an exciting rendezvous, the acknowledgement you lack from your partner, the distraction and escape you need (from yourself). The earlier episodes of the show really makes you ponder on all these things.

Also, you can really see that women are working on this show as they've captured the essence of what concerns and bothers women (in their twenties) so well. Be it the excitement, obsession and fear of rejection when having a huge crush on someone, the dejection when you try hard at university or work and are still left-behind, the urge to fit in and still feel disconnected with everyone. Really well-done.
The cinematography, pace, dialogues and background score also enhance the emotions and mood to a great extent.

As for the romance, the main theme of the plot, I think a lot of people might actually drop this series, because the story seems so relatable and doomed to be painful, too relatable even, for those who have experienced something similar and just can't cope with it anymore. And even if you might not agree with all of the female lead's actions and at times find her annoying and irritatingly irrational, she is still absolutely relatable, as you can literally grasp the train of thoughts that leads to these actions and decisions of hers. I further believe we've all either been in such a situation, were tempted enough or 'have this one friend' to/who despite seeing the red flags can't help overlooking them, knowing this might eventually crush us/them. Cudos to the cast for making our anxieties come alive.

Sadly, the earlier episode are by far better than the latter ones. At some point the story starts to feel repetitive and drained; there is no real progress and the authenticity and originality up until then slowly but gradually devolves into a clichéd run-on-the-mill romance, —outdated even — in which the heroine is (seemingly) stuck b/w two boys; although her final choice is blatantly obvious. Curious if there'll be an unexpected turn in the end. Also, there were some personal issues with an actor, wherefore his screen time was reduced drastically; reasonable, but unfortunately it took a toll on the quality of the drama.

All in all, this show had great potential — until the makers felt obliged to follow the 101 k-drama formula. Watchable only for the chemistry of the leads and the side stories, even though the ending is unfit imo and Song Kang's lack of emotions (blame the character) even make his pretty face boring.
And I urge you all to listen to the soundtrack, even if you don't want to watch the show: so fresh and SO good!

*EDIT*
If you've already seen the show (or do not plan on watching it) and would like to know why I felt the ending wasn't really fitting, see the comment section below this review. It's marked as a spoiler.