I can't really find the words to express why I love this drama so much so I'll try to do a very barebones pros and cons list instead:

Pros -
1) really great writing that will keep you engaged throughout
2) lots of satisfying character development
3) The ML - dude's a great actor playing a very morally grey and complicated person on a path to redemption
4) adorable FL, who goes on her journey of acceptance and healing
5) positive female representation, lots of good examples of female & male friendships
6) all the side characters are written to be very sympathetic, esp ppl like Areum and Ara; you empathize with and root for them
7) beautiful BGM and OST
8) heartwarming relationship between the leads, I shipped so hard

Cons:
1) villains are really evil & you'll grow to hate them, but they're not handled very well imo
2) age gap relationship, that's a bit rushed but YMMV
3) absolutely annoying SML who takes way too much screentime