Main reason I watched this despite its age, is because I like Hyun Bin as an actor and was curious about one of his roles from a bit further back.
I saw some mixed reviews, and although my opinion differ from those giving very poor reviews, I can't give it top score either.

I like the acting: I think Hyun Bin plays out his double role well. I am a bit more mixed about Han Ja-Min; I felt she "overacted" the sadness/weariness a bit at times.

As for the storyline, it got a bit too plot-heavy. I felt it could have been rounded off nicely at 12 episodes; I kind of expected it to be near an end in episode 10.

But: I must admit I got emotional (last 2 episodes).