This drama was really random and unpredictable, but that's what I loved about it. I know people had mixed feelings about Missing 9. This drama, at its core, is a comedy. Never forget that as you watch. The island itself is a dark place that tests human nature. You will see common themes like Nature vs. Nurture and Survival of the Fittest. In fact, they even mention back home (Seoul) as the happy place, so it would make sense that the scenes shot in Korea are more comedic and lighthearted.
Yes, it's kind of flawed and has its plot holes, but considering the original writer dropped out and another writer had to come in and pick up the pieces, it's pretty darn good. At times it did feel like different writers were writing different parts. It would go from Comedy to Horror to Action, for example. However, in the end, I think the last scene represented the drama real well as a whole. Basically, bright and colorful, but one hot mess. Beauty is in the eye of the beholder I guess.