I was in Busan when this show was in second week on air. Saw a lot of ads. First few episodes were less interesting to me but I became invested in episode 5 onwards.

What I like:
1) Parenting styles of 3 different families. Lee Mi-hyun is overprotective of her son Kim Bong Seok because of his supernatural powers but she never stops him from experiencing normal adolescence. He goes to public high school and he is allowed to bring friends home. Jang Ju-won becomes a single father after his wife passed away. You can see his dedication in raising his daughter Jang Hee-soo in safe environment. Lee Jae-man is another exemplary father despite his limitations.
2) Espionage - love episodes when Doo-shik, Ju-won & Mi-hyun were completing their missions. Even Frank's missions were thrilling to watch.
3) Acting - great acting by the cast.
4) Ending was just wonderful.
5) Romance stories of two sets of parents.
6) I am intrigued by the mysterious student who was not detected.
7) The battle at school. I love that Bong Seok carried his mum home.

What I dislike:
1) Higher ups at National Intelligence Services especially Director Min Yong-jun. Opening a school to identify and recruit superpowered individuals without being transparent to all parents is just a bad move.
2) I found the earlier episodes were less interesting because too much focus on Bong Seok and Hee-soo. Once the episodes focused on their parents' past, then I became more invested in the series.

Favourite scene
When Doo-shik was captured by NIS at Mi-hyun's residence and the scene at NIS.