I think most of us wouldn't be upset if it wasn't as abrupt as it was. Look at the last arc before this one, and how long Keun fought. What happened here was the classic buildup: we have a bunch of psycho cannibals and he's gonna have to fight his way out. Only... not? The main dude dies like a bitch after next to no fight, and then Keun is immediately killed. In ANY OTHER ARC this would AT LEAST be several chapters. Here? It feels like the author got bored and decided to flip the table and start fresh. That is what's upsetting.
Fair, can't argue with that.
I do think it may have been some sort of internal situation that made this strange "end", I do think too that if this had one more chapter this "end" would have been more gracious.
We probably will never know what happened, I am just happy that this isn't the true ending.. then I would be fuming in the mouth from rage, but as I can see something must have happened for this situation to pass and it was only one big flaw, I can accept it... but that is entirely a personal opinion.
My comment before was just me trying to not let too much discontent pile up to not sour everyone's mood, admittedly it could backfire and I could offend someone but I had to try... I just really love this story to not at least ease tension a bit.
In some time we will have the next series and we will see what Kishiro-sensei has planned.