Likes:
1) They really upped the ante for the CGI. It was a little fake for me in S1, but now it's high quality and believable. Easy now to get immersed into the world of monsters and humans.

2) Faster pace: S2 was edited well and I never got bored unlike S1

3) The addition of all the military scenes: I don't know if it's because I'm such a fan of the IRON SQUAD, but I really liked all the military scenes esp since some of my fav UDT guys from Iron Squad played minor roles. It added more action and intensity imo plus all the soldiers had such manly charisma that I admit I'm guilty of sometimes focusing more on their broad shoulders and sexy arms as opposed to the story ( 미안해 ¯\_(ツ)_/¯ ) .

4) Better acting: Every single character was believable. Go Min Si did really well with reflecting her toughness and longing pain for her brother. Jin Young did a great job showing the duality of toughness and tenderness with his character. Oh Jung Se nailed his role as the weird crazy scientist. Choi Go was impressive for someone so young being able to reflect devastation and bitterness so well. Lee Si Young 's agony looked so real. The military guys all delivered.

5) Jin Young's bulked up body. Those shoulders! Don't pretend you didn't notice!

6) A whole lotta naked butts

7) The world building: S1 felt a bit stagnant at times being in one apt building, but here we get to see more of the outside world. Glimpses of the monsters and nature. The movement helps the flow of the story imo

MINOR DISLIKES:

1) Too little screen time for Song Kang. I wanted to see more of his character as he was so central in S1. This season focused more on the other characters which I didn't mind as Min Si, Jin Young , and the military guys were fun to watch, but I wished there was a bit more time focused on the character of Hyun Soo.

2) Too little screen time for Lee Si Young. I just love her. I mean who can forget that back scene in S1 when she lifted herself up in the vent. She's the only actress that can literally fight and go head to head with guys. So I was kind of disappointed that she didn't have a bigger part in S2, esp in regards to action. She does have a memorable ending scene, but it wasn't enough for me. I wanted to see more!

3) I have to say that not a lot of answers were given and everything is still unresolved. You get a lot of new characters, but don't really understand their deal yet. Even so, I got hooked on the whole mysteriousness of it all. I'm assuming S3 will explain a lot of things so I can't wait!