If you are a first time watcher I suggest grabbing the Bluray version since it got few minutes extra content with every episode + small epilogue revealing a short emotional monologue or just a cute cut of a scene.
I knew what I was getting myself into yet I can't help but feel it's overrated. It's good but not great.

The good: Lots of talented familiar faces, big diverse cast. Great acting. Enjoyable contrast between the leads. Female lead personality reminds me of Han Ye Seul role in Couple or Trouble.

The bad: Long, really long! It takes forever for something significant to happen. Given its length, too much screen time was given to the main leads that the rest feels like less than a support character. You have a big cast full of diverse characters and mini sub stories yet barely anything shown from that. That's something I find modern dramas does better.
Male lead powers are problematic element that only leads to a weaker writing with plot holes.

The ugly: The villain character is just not good. It's the weakest part of the drama. Feels like there is a big contrast between how his character was written and the rest of the script.