I didn't watch this when it was first released, but I heard a lot of hype around it, as it's one of the top-rated K-Dramas of all time. So, I was concerned it wouldn't live up to the hype, but it did not disappoint at all! I have never had a K-Drama genuinely surprise me with as many plot twists as it had. I was on the edge of my seat each episode and could hardly stop myself from binge-watching. It was so good. Although I've grown tired of the reincarnation and time travel tropes recently, this felt so fresh and unlike any other. It's probably Song Joong Ki's best, but Lee Sung Min as the grandpa stole the show. He delivered such an award-winning performance. Truly had me thinking he was an old man! He somehow made me feel sympathy for this man who hadn't been the best person either. It wasn't just the writes and actors that made this a great drama-- cinematography and OST were brilliant too. Nearly a perfect drama. I felt a little mixed about the ending. Compared to the rest of the show, it was almost anti-climactic. It was not terrible, though. Some might feel differently than I do.