I feel that session 1 characters have more "personalities". Session 2 focusing more on the character personalities changes and not so much into the "politics"
Prosecutor Seo changed from the tactful person in session 1 to cunning, busy body like salesman type in session 2
Hwang Si Mok also changed, he can yell and smile in session 2!

Session 2 pacing is better, faster compare to session 1.

Story & mystery wise, session 1 have heavier topics and give more surprises compare to session 2.
I can say session 2 is lighter and more towards entertainment, session 1 can be a bit boring for some people, but having more content and given an impression of more well prepared compare to session 2.

Still thumbs up for all the actors and actresses acting.