To quote the two Sanbun Kyouden related post in MAL:
"After reading a few of this mans(woman's?) work, I am close to slashing wrists...
..can't believe I''d ever read manga that'd make my blood boil...even for hentai"
"This guy knows how to make people rage...
..must have been brought up by an abusive mother and sisters as the way he depicts his women, even for hentai, is so degrading that even I feel ashamed for being male at times"
Both of this came from one user named obliviousz (http://myanimelist.net/profile/obliviouz) but really if you have read Zain it probably won't shock you much to find out that someone would have this
opinion of this author. (Despite his works being very in demand and having enough of them translated to English, he isn't really stirring much controversy which is probably for the best as Zain is one of the best manga out there even if you remove it from it's H category but at the same time, it's what makes it difficult to gather an online sample of what English readers felt about it as a group.)
Normally such comments are non-notable especially for hentai where you can never tell what limits of depravity a complainant has dwelved into the category. (Many whom can go to the deepest levels of desiring guro, futa and the ever popular tentacle rape where as others may have a vast knowledge of ecchi to middle of the perversity hentai but still not realize there are hentai in this category.)
In this case though it's notable especially this phrase: "..can't believe I''d ever read manga that'd make my blood boil...even for hentai" because it not only sums up the series but it is what pushes Zain into masterpiece territory.
Now those looking for an extreme hardcore disgusting hentai won't find it here. There are a lot more disgusting series than Zain. Similarly those thinking "even if you remove it from it's H category" plus the 10 rating may mean it is on par with such works like A Clockwork Orange or Saw (only the 1st one) in terms of depravity may also be disappointed to find out that Zain is much much worse in generating a disgust for it's characters.
Now whether you would consider Zain's plot to be smarter or dumber than the mentioned two movies is up in the air. However if the question becomes a question of which series moved me best then Zain wins it hands down.
Albeit the manga format does help Zain feel less of an LSD trip but it's the pacing, the artwork meshing with the story, the pathos combined with the general theme of Sanbun Kyouden's works that makes it truly stand out despite the generic if not "been done before" plot of the manga.
Speaking of plot, it may seem like I'm withholding the plot but if anything Zain is the type of plot that a reviewer no matter how good or bad should abstain from "describing" because it can only distract you from noticing what makes Zain stand out.
If you need some form of clue, a synopsis of Zain could easily be about beastiality... but then if you come in expecting a beastiality manga, there's a good chance you'll miss out the "family chemistry", "slavery" and "psychologic" impact Zain "excels" at.
It's not that typical hentai manga readers aren't familiar with this themes being mixed in hentai plots but this is a type of series where there's a huge difference between "noticing" and "noticing how it excels".
Again, this may seem like I'm being vague-ish but Zain is the type of masterpiece that can affect a non-H manga reader or a light to medium tolerance H manga reader differently from a reader looking for depth in their H manga in ways not only relating to your tolerance for rape, slavery, beastiality but really your H manga tolerance for Zain.
Still, if you have read at least more than one of Sanbun Kyouden's work --- all the above: they seem like it describes all of his works especially if you are more on the level of obliviousz' taste but for those who doubt Zain is... less special or more on par with his other works, one can be helped by this comment by an IMDB user of why Eternal Sunshine of the Spotless Mind is one of Charlie Kaufman's best works:
"Because it's the only Kaufman script that doesn't completely unravel in the third act. Kaufman is a brilliant, brilliant writer who has come up with some amazing ideas, but he doesn't know how to sustain a good thing through three acts. Being John Malkovich was utterly bleak - so much bleaker than the first two acts, that the end is simply too damn jarring. Adaptation creates a running gag about Kaufman being unable to write a third act, and then proves that assertion true, by dovetailing into pure ridiculousness (the fact that Kaufman turned it into a joke doesn't make it any less true).
Even Kaufman's Synechdoche, NY script starts to fall apart in the last twenty pages or so. And I'm not slamming the man. I love BJM and Adaptation, and I thought that, overall, Synechdoche was a fun, thought provoking read. But Eternal Sunshine of the Spotless Mind is Kaufman's only flawless script, imo. Maybe due to Michel Gondry's humanizing, uplifting influence, more than Kaufman being left to his own devices, but that doesn't take away from the accomplishment.
In my opinion, Eternal Sunshine of the Spotless Mind is one of the few movies ever made that is almost flawless in every respect. Kaufman's other works are amazing, but also flawed. I would argue that all of them belong on any top 100 let alone top 250 list, though. "
Although I haven't read all of Sanbun Kyouden's works (even limiting it to the English scanlations), from what I have read Zain could be Sanbun Kyouden's Eternal Sunshine of the Spotless Mind.
Note that the series does unravel by the end and you won't get a typical feeling of "plugging all loose ends" but this is also what separates Zain from Kyouden's other works. One comparison for this is Basic Instinct's open-ended ending but Zain goes past beyond that by offering less.
This is why Zain is a masterpiece. It is one thing to say all I have said above and say ok this is a 10/10 series it is always another thing for a series to be rated 10/10 because it is one of the most unique and strongest executions of storytelling that it impacts the reader beyond "the theme" beyond "the plot premise" beyond "the characters" beyond "the artwork" and if removed from it's medium of choice, it loses more than what would normally be lost in translation from the adaptation process because the whole thing just forms a harmony with each of it's category - beastiality, h-manga, slavery, rape...and yet it does it so well that it also surprises if not impacts the feeling of it's reader regardless of their prior knowledge of how original the scenes were.
I'm sure that last paragraph above has been felt by many fans for their own beloved series but this is why Zain needs to be a 10 regardless of the hate or apathy or disgust or even disappointment for the lack of extreme sex scenes (outside of the beastiality scenes) each individual reader of Zain may have because no matter how one would like to downplay it...Zain did meet the category of a series exceeding it's category and alienating it's readers without cheapening it's universe. Such thing can only deserve a 10 not due to being outstanding but for being a true "masterpiece".