One of the most engrossing K-dramas I've watched in a while. I liked how it combined alternative reality with actuality, drama and suspense. Its technological focus is executed tastefully (i.e. without the cringing 'technonerd' stereotypes), and the romance element weaved itself through the plot without throttling or dominating it. I was also pleased that Chanyeol Park portrayed an introverted programming prodigy with sensitivity and, again, without the trite stereotypes. If there's one criticism, it would be the slightly illogical ending that I felt didn't explain the resolution that clearly—but overall, this series is very thoughtful, realistic and well-written.