Part 1 had its problems and was not bad as it had a real gripping ending, but part 2… what were the writers thinking?

I don't know how important CSAT exams are, but this exam is one of the driving plot points of part 2. What makes no sense is that humanity faces extinction and yet all these kid could think about was getting into college. I am sure there are more important things to worry about than college entry at a time like that. This becomes such a central plot point that one of the characters literally goes insane after finding out the 2023 CSAT exams were cancelled and were to be held in 2024. This leads to the drama ending not to a final showdown against the alien threat, but the final boss being this kid who has gone insane and had somehow activated god-mode in his final rampage.

The ending was anti-climatic and skips ahead to 2024 where humanity has wiped out 99% of the menace so had the threat under control. Okay... so we are supposed to imagine the final desperate struggle and not be shown it? Instead we were given teenaged angst drama with automatic rifles? Sure.