Very interesting is what I would like to say, this isekai takes itself seriously, is uses logic to drive the story and makes sense for the most part. The story is that of a kid with some traumatic past we (as of yet) don't know of that left him apathetic and indifferent towards others, he's the kind of guy that weights pros and const and tries to decide things in the most effective way posible even when it might be in the grey zone in terms of morality, he's not an amoral character. The setting is that he and others are transported to an isekai they initially know nothing of to solve quests, kinda like Gantz but fantasy and less gore. After the quest is done they have some free time and get transported for another quest and each quest increases the participants by one. Also, this quest vary and can be of different kinds, from save a village to deliver something, kinda like a random guild quest which of course gets harder each time, it's not a death game type of story, thou it's not clear what happens if they don't clear the mission and more than that would be spoilers.
So story is not bad, chars are varied and say one secondary char increase per mission, so far (6th mission), other the MC, 1 is interesting, the popular through hard work type but with a heavy past, one is ok, thou annoying at times, and 2 are the kind you want to see the MC put them in their place, not because they bully or are lowlifes, the opposite, they are they kind that can't do anything but spout platitudes and get others in trouble because of childish ideals, and they don't learn. The MC on the other hand is great, cool headed to a point you could call him cold and insensitive, he doesn't give a sh*t about the others unless he has a reason to or can rationalize one, it's not completely clear, he can't stand the other two idealist BS but he doesn't say anything, he doesn't even care enough to try to change them and, it's not that he has no emotions, it's more like he kills them, there is something there blocking his path to a more normal life.
Also, art is good, fights are good too, dialogues are decent and the MC inner dialogues are quite good.
Unfortunately, it was going great till the drugs cartels arc, which is to put it simply, extremely boring and completely out of touch with the rest of the story so far. It's seems to be written by someone that has as deep understanding of the issue as having watched a marathon of Narcos, the author is out of his depth here. Also considering how manga works it'll be the longest arc so far (and I was right unfortunately), this arc has the about the same length as all the previous arcs combined and it ain't over yet (ch 44). This arc was so bad that I'm surprised the manga didn't get axed.
Edit: The mix of serious and heavy concepts and actions taken (like at the end of mission 5) with the characteristic immature idealism that Japanese often express in manga is really bizarre.