Great cinematography, literary technique, and a very tight character development script. If you're a literature nerd, you'll enjoy analyzing the foreshadowing, the throwbacks, and the parallel structure in many places.
You'll see major motifs getting called back from time to time to help you understand characters better or signify their development. The writing was also super consistent from start to finish, and loose ends were tied up really well. I love how the story started with mean questions at a talk, and ended with mean questions at another talk. This is the type of production I love to see.

Yes, just like everyone else I got the second male lead syndrome, but the love story isn't the main point here. The writer put so much more emphasis on the grandma x Ji-pyeong "fake family," the Seo sisters + family, the Ji-pyeong x Do-san bromance, etc. I'm especially a fan of grandma and Ji-pyeong... the human aspect of this drama is amazing. Makes me wish I had a grandma like that (cries a little

If you're a cameo-chasing nerd, you'll also enjoy the special easter eggs they threw in. Like the 2 Days 1 Night guy playing a security guard, or Lee Bo-young (female lead of the scriptwriter's previous drama I Can Hear Your Voice) at the bar, or Yeo Jin-goo's voice as Young-sil the AI...

To summarize: Watch it for the production value. Watch it for the family drama. Watch it for character development. You'll love the show.