You'd be surprised; porn is what initially hooks people in, yeah, but what gets them to stay is the gameplay/story/art/audio.
We've got a Discord with over 3,000 people in it, and honestly, 90% of the time the discussion is people talking about the plot of the game or showing off gameplay challenges they achieved (like beating the boss without being damaged), very rarely does the discussion on the Discord turn to porn comparatively.
Same goes for other forums the game is discussed on; even this thread has a lot of people discussing gameplay or plot or other aspects that aren't directly about the porn.
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In the East, a lot of porn games are there for the porn, yeah, but people also love the characters and plots and gameplay for those games. We'd like to follow in their footsteps with having people enjoy the game as a full fledged game, not just something to fap to and forget.
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Additionally, about 30 or so years ago, violence in video games was a hot button topic that was used to hook people into video games, but was often used in very blunt, excessive ways, where 80% of the game would just be gore and 20% would be actual gameplay and content outside of that.
Over time though, people started using violence in video games in ways that made the game's story or gameplay or some other factor more interesting, instead of wielding it with a big blunt stick, they chose to use it with smarter implementation and to not make the violence the core factor of the game, but just "a" factor, one piece of the big puzzle that made up the game as a whole.
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That's where we feel adult games are headed too; in the coming years, you'll likely see more and more games where the sex is a significant aspect of the game, but not the aspect that the entire game revolves around while ignoring gameplay, audio, art, story, and so on.
(We're not kidding about the significant part either, we're at around 160 different sex animation loops in the game so far, with no palette or model swaps or anything like that, should top out at around 210 or so for the full game)
We'd aiming to make games like that though, for Future Fragments to be something that people may pick up for the porn, but continue playing for all its other aspects (as well as the porn, still). There's a lot of other games going this way too, like
Crisis Point: Extinction, for example.
Don't get me wrong though; we definitely can and are improving on the game before May 2020 (our release date), and we'll definitely learn from our experiences on FF and use those to try and make better games than FF with the subsequent games we make, too.