Re: Hentai - Story vs No Story
If we aren't excluding the less typical understanding of the idea of a story/plot, than separating the Hentai and the story is strictly impossible. Even the most basic of H has some form of content, which inevitably has a situation it depicts (e.g. ‘tentacles binding and fucking girl’), which, itself, is a self-contained micro-story(e.g. ‘girl is having sex with tentacles, was not intending to by look on face and expression of body’). The plot is not necessarily one which says much; you're not likely to find the ceiling of the Sistine Chapel here - but the work still nonetheless tells a story.
If we are using a more typical understanding of a story/plot, my answer has to be much the same as BlueShinobi's one, in the most basic sense. I would not merely strip all context from a work of hentai simply for its titillation - even most of the more base pornographies have at least a touch of scene-setting before the action starts, for quite human reasons, which I won’t bother elaborating on (it would take too long to do so). That said, while context, plot and story are things that I would not take from hentai as a general rule, I find that a hentai’s story commonly does more harm than good: there are stories that work well with hentai, and stories that do not… and, unfortunately, most hentai seem to include a plot of the latter variety.
To put it the most simply, all works of story intend to elicit a response in the reader; mysteries intend to harbour intrigue, dramas to foster concern and sadness towards the characters, horror to induce fear, action and adventure seeks to fascinate and thrill.... while hentai, and it's similar cousins, are intended to inspire sexual arousal. Now, it's quite possible for a human to feel several different emotions (for lack of a better term) at once, but at the same time there are several feelings that conflict with each other - sadness and arousal are a good example. This is why I find that, no matter how good the story is, when the subject of the story conflicts with the hentai's intention to titillate, the sex and the plot only hurt each other.
Those visual novels that are lauded for their storytelling come to mind; the ones that make you cry and feel for the characters may certainly have very good storytelling, but I suspect there are considerably fewer people who laud the whole story as legitimately erotic. In most cases I have seen, the story and the hentai seem to take turns - the story will be initially prominent, have a gap for the hentai, return to story, hentai, story... in the end, the fracturing of content only ends up interrupting the mood that each of the elements attempts to build, inevitably creating awkward moments in which a person must abruptly adjust their mental state from one to the other.
A story to a hentai can be a good thing, but only if the intention of the story and the intention of the hentai work together. Sex Demon Queen is a brilliant example - the story intends to amuse, which does not conflict with arousal (when used correctly). I would hate to see a neutered version of Sex Demon Queen with only the H-content, because the story actually adds to the overall experience.
Well, that’s a quick summation of my opinion, at any rate; I could go into more detail, but I’ve covered the important parts, and I’ve told myself I’d keep this short. Hopefully, the intention behind the text is clear enough.