This series is a gentle and quiet exploration of identity and self in adolescence. I'm not sure though, which age group could be the intended audience -- teenaged people who get a mirror for their own growth or older adults who might feel a slight melancholia when watching the drama.

All in all, it did not wholly deliver on its promise.
The premise I liked, four young people who have to come to a decision and their own standing point regarding their position towards platonic and romantic relationships -- and issues of belonging to a group versus being who you are. Even the love triangle made sense within these topics.
The execution, though, is stilted and at times too slow.

These are definitely directing choices, not the problems of the actors -- as soon as they get to do something, they start to shine.
For example, I don't understand why the actors stand right in front of each other in most conversations, with their arms hanging down without movement (and the whole drama is conversation-heavy) -- alternatively, they talk while walking next to each other at a snail's pace. I suppose the director wanted to convey some kind of awkwardness -- which is a good idea, since the characters definitely don't feel comfortable for most of the time, but it just gets boring after a while.
Also, the characters (with the exception of Namgoong) all have similar mannerisms (or, if I want to be a bit mean, the same mannerisms) -- including the teacher, which I mistook for another student in several scenes.

There were also some minor issues:
* At times, the background music did not quite fit the mood -- I'm also not a fan of the "plink-plink"-kind of music.
* The scene with the adult toys in the beginning was never resolved, and did not fit in with the rest of the story.
* I could have done without the kiss at the end -- it feels as if the writers or the director said: Oh, the audience also wants a kiss, so lets add it somewhere. A hug or some light cuddling, or even sitting very close to each other would have fit the overall mood better.
* I'm also not too sure about the female character, but since she had her own story arc and character development, I'll let it slide.

The plot itself, with its theme of exploration and the awkwardness of navigating relationships in adolescenece, is fine, and surely of interest to many. It's just that the way the series is brought to the screen cannot convey all the depth and the emotion it wanted.
Maybe if the creators had been clearer of the intended audience and made some bolder choices for directing according to that, it would have been more on point.

Overall, I found it okay to watch, but not worth a second time.

[This is an edited version of the review I posted on Viki.]