For the first season (eps. 1 - 6), the story focuses more on their survival from the aliens' attacks. While the second season (eps 7 - 10) focuses more on their togetherness after more than 1 month fighting.
The storyline is good but missing a lot of things, such as where the Won Bin in the second season was, where the 3 survivals found during eps 6 - 7 were. did they evaporate or what? They just disappeared without any story.
Things that I hate are the students are stupid! they know the aliens are stimulated by sound, but they love screaming, shouting, and yelling. My ears almost popped every time they have intense argument.
Even the smartest student, who only focuses on SCAT test, is the most stupid! How can't he use his logic? There is no chance any test to be conducted when your country is busy with life-threatening war. Even the committees might be dead already at that time! so frickin' stupid.
Oh yes! they do not change in term of characters and mindset after one month passing. keep whining to go home! for what? everybody is dead. you cannot even survive alone!
Your emotions are really challenged here not because the storyline, but how dumb the students really are. Just few are the mature.