Kamisama no Iutoori is an underrated manga that one would read only by sheer luck, it's not well known but it's better than most popular manga out there.
Having discovered the manga by recommendation, i would never cross paths with this unique and bizarre take on the survival genre. You are not prepared for what the manga brings to the table, but you'll enjoy it more going in blind. So if you are in doubt about reading it, let this review clear some things up.

The story is what keeps you going, a high school survival manga with just enough weird elements that grabs your attention. A cautious note, is that the genre leaves a different taste for everyone, some like the thrill and the fantasy of being in that situation, an escapade to the story that's being told. Others feel its just a bizarre action oriented fest.
With just 21 chapters you are going to breeze through it, it doesn't overstay its welcome, and every chapter leaves you pumped to read more, it's fast paced, but not rushed per say. The weakest part is probably the explanation for why the games are occuring, it's left ambiguous, but it's not a huge problem, keeping in mind that a sequel exists (that's not as good) and so some questions are left out unanswered.

The art is good, not that special at first but as you go on it gets much better. Akeji Fujimura's art is really intense as he polishes his style later on, and it suits the dark tone of the series.

The characters are probably the strongest aspect, the thrill and fear for what is going to happen to them are a selling point, because they are all interesting and everyone has a distinct personality. The dynamic between Shun and the rest of the cast is phenomenal, the only thing that lacks is more development, but for the manga's length we get a vast cast that's different enough that keeps things interesting.

Overall this is a fantastic ride from beginning to end, and for a survival manga it doesn't hold your hand and isn't playing it safe. Bizarre enough to keep your attention and the right amount of chapters so it doesn't drag on. The ending is also well executed and keeps you hyped for what's coming next, so don't worry about being disappointed in the end.