It's not everyone's cup of tea for sure, since the lead couple are not ordinary and certainly not young, but they are among the most realistic couples i have seen in Kdramas.

Story:

Star math teacher. Heartthrob, rich, whatever you name it, he has it. There are dark secrets lurking around. there is also tragedy but filled with many good moments. On the other hand, we have a very troubled family with a secret of their own. not to mention the hardships and happiness shown are meant to depict a more realistic feature of life. Students' pressure in life. A world where justice has no say in it and the hierarchy of relationships. This is how real world is.
Not many loopholes and certainly everything wraps up perfectly. The story at its core is flawless, except for a few short mishaps.

Acting:

First time seeing the leads. They are mature in both acting and delivering a decent character. The chemistry is off the charts. silly at times, but beautiful. Wish they had more interactions as a couple, but this drama is more heavily focused on the story revolving around students.

production:

top-notch. The locations used for shooting and even the items of clothing worn by the cast is chosen with dedication and care. It's not just some low-budget drama. everything is on point.

soundtrack:

Beautiful songs are used throughout the drama. totally matched the mood.

Overall, if you like the Genre of teaching, students, family, and a mature romance, this is for you!