I'm writing this review for everyone that doesn't feel like watching this because the cast changed.
I was also upset, when I found out the main leads would be replaced (actually they didn't want to come back, the director did everything he could) but since Lee Joon GI was cast, I gave the drama one more chance and IT DID NOT DISSAPOINT.
Most of the actors from S1 are gone, but the new ones actually studied the characters and imitate the same mannerisms and keep the same energy, which is good. Also, they added names, every time they showed up till the end of the season, so people won't be confuse who are they.

The storyline is still solid, the Taelha and Tagon character's don't lose their shine. Saya, Tanya and Eunseom have their character development too.

Keep watching.