It was everything! The story kept you on edge, and the acting from both ML's were so good. We were introduced to Yeo Jin-goo through this drama and have since almost watched all of his works. Such an awesome actor. The story keeps you guessing until the very end and it's worth it. The last two to three episodes will spike your anxiety, and then give you a bittersweet ending.
We will say that not everything may seem as it is with Han Joo Won (in a good way).
He honestly does everything because he works by the books.
In the start, we thought he was either working with his father or had it in for Lee Dong Shik.
The OST was also brilliantly done. It only adds to the emotions.