Edit: I see that some people actually like having to grind for 8 hours to get any sex scenes. Weird, because whenever I see a WIP exhibitionism game with no sex scenes everyone keeps crying that they need sex scenes now!
A bit of gameplay never hurt anyone, if you just want the sex scenes regular porn & hentai will serve just fine. But there's a bit of a thin line between gameplay obstructing the adult aspects and gameplay contributing to it. Naked order had gameplay contributing to it, it was centered around buildups, you'd have to play this little minigame where you gotta sneak around outside naked withou being spotted too much, or getting caught and raped (or I suppose you could do that too, you know if u just wanted sex scenes NOW, hmm?)
And at the end of it you'd be rewarded with some adult scene. As the game progressed those scenes gradually got more and more extreme. You're rewarded for your role in guiding this girl on the screen down a path of ever increasing degeneracy.
Putting in some work is part of the fun, why do you think people like Dark Souls? Cuz it is easy? It's because it's challenging that the rewards for success are just that much sweeter.
Making a good hentai game seems to be a delicate balancing act to find how much story is too much story, how much gameplay is too much gameplay, how much sex is too much sex; because that can actually be a thing too. You gotta have some story, but not so much that it'll bore the player (because nobody really plays hentai games for the story; looking for a good story in a hentai game is like looking for a good meal in an office, you know there might be some remote possibility, but it's unlikely af.)
You gotta have some gameplay, because otherwise how can you really call it a game? Is it gonna be grindy? Of course it is,
all gameplay is grindy. To a varying degree anyhow. And again, you gotta find the right balance of grindy so the player won't get bored.
Then lastly is the sex, the sex has gotta mix well with the gameplay and the story, they need to form a sort of triangle, a gameplay loop, story leads to gameplay, gameplay leads to sex, sex leads back to story, and so on. If the sex seems to be taking away from the story or the gameplay, that's probably because you have too much sex. It's very easy to resolve too much sex, for instance in honey select the gameplay is mostly in the sex, you have stats on the girls, you fuck them to affect those stats in the direction you want to groom her into the perfect fucktoy. The sex becomes the gameplay, easy fix. Iif that game had some other fun gameplay in it thuogh, that might still be too much sex, because it makes you spend 90% of the time fucking the girls leaving anything else in the game pretty much relegated to the background.
You gotta look at why people are playing hentai games, instead of watching hentai, looking at hentai pics or reading hentai doujins and manga. There's a bunch of possible reasons, one of the simplest ones is fun, games are fun, getting fun and pleasure all in a single package is great, couldn't be much of a better package right?
There's also others that might just not be satisfied with porn, they want something more interactive, to immerse themselves in it rather than being passive observers of it.
Others still want to make use of the victimless crime aspect to watch or enact some sick shit on their screen with nobody harmed in the process cuz it's all just a game and all in good fun in the end.
And I guess some people want a good story to go with their porn too, but those are as rare as the hentai games that contain good stories.
Whichever crowd you're trying to please, as a developer, you have to make sure that your game would appease them, and it's a delicate balancing act between the 3 elements, the gameplay, the story and the sex, and the reason 90% of hentai games suck ass is because most of the developers fail to balance these things, or even realize the need for such a balance. Which makes games where these things are balanced stand out so much.
What balance works best depends on the player. Some players are best served with sexual content 100% of the time throughout the gameplay, some players are best served with sexual content only 50% of the time, maybe a few only want like 10% sexual content.
But ultimately it all goes back to this being a game, and a game needs to have gameplay or it isn't a game anymore, and if u don't like gameplay, you shouldn't be playing games, just reading doujins or watching hentai like a normal weeb.