Very unique execution, as the two time periods in the show each take up half of each episode. I enjoyed how the drama shows us the story, rather than tell us, through this unique execution. Acting was solid all across main and supporting cast members as well. This is definitely sci-fi thriller and mystery with a healthy fix of romance and bromance. Lots and lots of praise for this since I haven't seen that many sci-fi premises in kdrama. Check it out even if you aren't a sci-fi fan. I was very impressed by the graphics in this and felt the drama was of movie-production quality. Recommending to all my non-kdrama watching friends!