I am on ep 5 and i just want to say this drama is amazing. First of all the acting I'm not familiar with the leads but they are doing an amazing job at portraying emotion.
Right from the first few minutes the drama starts with suspense and introduces you to the plot in the first episode it contains flashbacks that add to the plot rather than take away from it.
I cant say much since I've only watched 5 episodes but I highly recommend it it will keep you at the edge of your seat and feels very realistic despite the plot being sci fi related