This manhwa had an interesting beginning, an interesting middle, and an interesting conclusion... of three different stories chopped up and slapped together into one, that is. In other words, the beginning does not match the middle and the middle does not match the end.
As others have remarked, there is inconsistency in the character development- you literally have people turning from "good" to "evil" or from "evil" to "good" in the span of a couple chapters with no explanation whatsoever about their abrupt personality change. One particular character springs to mind as being nice in one chapter, super evil in the next volume, nice again a couple chapters later, evil some chapters after that, and ended up as a saint. And no, he was not possessed.
Now, as someone said, stories are supposed to evolve, but just as a dog cannot evolve into a bird in 100 years, this story should not change from fantasy/horror to political commentary in about 30 chapters. It was just extremely bizarre, and as a result neither the fantasy/horror plot nor the political commentary plot were fully elaborated upon. The origin of the demons is not known, and the problem of the demons attacking the protagonist vanished after ~15 chapters without any sort of explanation other than "and they are gone timeforanewstoryyay". The political agenda was way too forceful- I've seen more subtle cartoons in The Economist, and such political overtones did not show up until the latter half of the manhwa which makes it seem like an afterthought rather than planned out.
The characters were extremely static. There was almost no change in the protagonist from the start of the manhwa to the end. The only difference is that her "mean attitude" at the start of the manhwa was inappropriate because she was a teacher but her same attitude was appropriate at the end because she was dealing with political corruption. Even Pan, the most enigmatic character just faded in and out of the picture, often showing up just to kill demons for 2 panels and then disappearing. In the end, there was almost nothing explained about him. Other than the couple characters that had 180* personality flip flops throughout the manhwa (and some of them had gender flip flops too), the rest of the characters did not evolve or progress throughout the course of the manhwa. Mostly it just seemed like the author kept introducing more and more characters to play a designed role and then forgetting about them later.
Back to the political commentary- I have always been a believer of "less is more". This manhwa was pretty ruthless in its depiction of the evils of a certain country while maintaining the purity of another certain country. Then, every couple of chapters, the author would insert a page of disclaimer-esque dialogue that said "oh but we are all equal" and "violence is bad", but then continue for another 30 pages of very blatant painting of the evil of the aforementioned country yet again.Closer analysis of the manhwa will show that there is clear bias for one side over the other and any dialogues saying otherwise rings very false.
One the bright side, the art was good and the fighting scenes were good. Everything else was just all over the place without any real plot cohesion. I, for one, was relieved that it was as short as it was, so that less of my time was wasted reading this. The plot itself is fundamentally flawed so I will kindly disagree that dragging it out for another 10 volumes would have made it much better.
If you want good art, action, and a solid plot, do yourself a favor and go over to Shin Angyo Onshi by the same author(s) instead. If you want action and political commentary, go over to Akumetsu or Sanctuary. If you just want some zombies, try Dawn - Tsumetai Te- or even Highschool of the Dead is better than this. This manhwa is seriously in the "skip unless bored and out of things to read and just want to kill time" category.