I honestly don't catch the reason for some people rating so lowly this show (I even found a 1/10 - lol!).
Is it for the violence? Well, not your genre of show to watch, but not a reason to be so negative
Is it for the scenes of tortures? Well, not your genre of show to watch, but not a reason to be so negative
Is it for the sadism? Well, not your genre of show to watch, but not a reason to be so negative
Is it for the madness of some? Again, not your genre of show to watch, but not a reason to be so negative
Some should look at the quality of the product, without approaching it expecting a fairy tell or a romance...
That said, this show is good, even if not a masterpiece. The characters are well sorted for being part of this sort of psychological experiment, showing different kind of personalities and their evolutions alongside the development of their prisoning. According to literature based upon similar experiments really happened, the story is coherent, to include also the devolution toward violent and sadist behavior till the use of torture (with scenes inspired to The Orange Clockwise). What you watch is disturbing, disgusting, cruel, insane, perverted, sick. Which are exactly the feelings that any normal (?) being should feel. This is not a show exploring the good feelings, instead the obscure insanity which can unexpectedly show up even from people apparently sane when in specific contexts. Which is not specifically tied to a confined, I might say prisoning space as in the show, but generically to extreme conditions, the same that a hard crisis (because of a war or similar e.g.) can bring or the same where the social order is based on a strong inequality, where those managing power can easily turn to psychos, showing sick behaviors. Situations within which the humanity of each can be overwhelmed by the insanity. And actually this is what happens in the show. On a side an audience made of an elite of superrich psychopaths looking for extreme sensations. On the other side a team of assorted human beings and personalities, all together ending up to insanity in the end. Only the death is able to break this sort of collective enchantment, bringing all of them to a more normal condition (but actually: what can be considered "Normal"?).
To be honest, an ending that I found weak, since it still relates too much on the humanity of the people in general, and that in our reality is looking like a too much benevolent approach: just watch a news...
This is not the only thing I did not like a lot. Another one relates to the exploration on the past life of each of the eights. Only for "3" the reasons which pushed him to take part to the show were better explained, while the others were just roughly outlined.
All in all, it's a good show, with a well casted assortment of nice actors, a good direction, an original and effective setting.