Headline says it all. Perfectly contained story that's easy to follow and doesn't leave any noticeable holes, doesn't require suspension of disbelief, doesn't rely on plot convenience, doesn't leave characters' motivations or actions confusing or questionable.

And we get a bonus: a potential ending leaving room for a season two or spinoff.

Some bits can be a little bit predictable once you've seen a kdrama or two like this. But the turn of events still leaves a little surprise that'll keep you watching for what happens next.