Let's be short the story on the 15 episodes wasn't a revolution but was good enough, the construction of the world, the revenge, how he accepted his new life, the bittersweet comparation between his past self and his new life, how he missed his old family, sometimes the characters were plain stupid just because, but they were evil so it was fine as we watched them fail and suffer.

The romance was not there just small moments but was fine until ep 15.

The best of the drama is the relationship between Jin Do Jun and his grandfather, is pure gold, it's just perfect and deserves a 10 just for it, the acting was on point even with the child actor was stunning. His family aka brother, mom and dad where wholesome too, as the family he never had.

But the ending ruin everything, they throw away all the development, the dreams, the hard pushed love line, the promise with the grandfather.
JDJ became by far the saddest character in the drama and overall the ending is disappointing, not satisfactory at all.

The first 15 episodes are a worth watching but the last one is plain wrong.