A character focused take on the Sci-Fi genre. Korea doesn't typically have the budget for this kind of series and it was really well shot and made. I didn't feel like the plot ever dragged. The pacing was faster than a typical drama and there weren't any unnecessary shots or fanservice. For instance, many dramas have 30 seconds of people staring at one another from different angles. I thought that the science they were trying to portray was realistic enough that it didn't take me out of the story. Some viewers might complain about how the characters interact or how the story unfolds, but they aren't keeping in mind that Koreans have very different dynamics with other people in society. So keep in mind the differences in cultures when viewing. As an avid Sci-Fi fan I didn't feel like this series "ripped-off" anything else. Some technology had Alien vibes but that's where it ends.
Also this is based on a short film, and I personally really like that is was made into a entire series because it built up the tension and gave just enough information for you to want to find out more. All and all well-contained story, it doesn't need another season.