I really love this wonderful drama. At first, I did not want to watch it because of the subject matter (Secret love affair between teacher and student; married mature woman and young man; etc). But after discovering Kim Hee-Ae from "The World of the Married" (where she acted so well), I decided to watch this drama too; plus I love Yoo Ah-In's visual and acting in period drama Jang Ok Jung. The starting, I thought it was slow and boring, but as the story progressed, I got hooked by the piano music and the relationship between the main leads, and binge-watched this in 2 days. The acting and performance by the main leads were excellent, their passion for music and for each other was so intense and incredible, and I LOVE LOVE the classical music played throughout this drama. It made me love piano classical music again. This drama has a mature theme, and it is not for everyone.
But if you like classical music and forbidden love theme, perhaps you can give this drama a try.