I don't know how to start but, let me tell you that I am still in Ep. 5 and I want to share my thoughts while I still have it. This will be my initial rate but, it may change once I finish the drama.

Acting wise - I have no complaints for the cast's acting since they are always brilliant. ML has been my fave for a while now, especially from his movie "tune in for love". He can naturally act, the way he conveys his emotions thru his eyes which is a mark of a very good actor. FL, I haven't had the chance to explore her dramas which he plays main role but, I always admire her in "Love in the moonlight". and watching her in this drama is never a disappointment.
Kang In-Wook (Kim Sung-kyu) undeniably a very good actor since I watched the Kingdom series.

Music score - I love all the songs cause it always gives you the real feeling in every scene, it helps you find the emotions.

Plot - From Ep. 5: I wish it is more realistic. The AI is somewhat questionable, well I got a lot of questions while they are using it. A device is as good as the information you feed them. It seems like they feed them feelings and inner thoughts of Ji Su and it is kinda off for me. This does not stop me from keep on watching it though, I will just ignore and play along as if it is doable. This could be doable if the creator is high and mighty.

That's a piece of my mind on this drama for now. I will sure return to complete my ratings and review. Overall it is enjoyable.

Edit: And I have returned after 24hrs. I have raised my rating to 8/10, some of the plot can be turned a blind eye on it, don't rationalize it :). The story still gives me the warmth and forgiveness. Highly admired Ha Won's character because he is a really kind and compassionate person. He loved with all his heart, know when to stop and move on, not filled with anger and very forgiving.
Seo woo may have the positivity in her but HW has the best character. Go ahead and watch it!