You've added another category, Mature. Lol So is it Mature to Adult to Porn in the US. I'm in Europe and we're abit more laissez-faire when it comes to nipples and willys.
I did read a lot of romance paperbacks, well all my Mom's ones under the cover of darkness. They're filled with racy smut!
My argument here is that we ALL want an Adult game over pure Porn. Not only do we all want that, I think it's mechanically impossible to make a pure porn game. It would turn into a non-game.
Eh, there's slave trainers and pusooy games that are literally you just causing sex to occur. Then there's games like Man of the House, or worse, Absolute Power, that are just a premise with some characters and then nothing but grind for a sexual reward. Porn has a premise. I watch incest porn all the time. But the distinction that sets these basic character setups apart from what we call, adult, is depth. Does your game tell a story, does it have fleshed out characters with their own motivations, is there a goal?
An example I've used to show why games like Man of the House and Big Brother fail to be anything more than porn games, is a comparison to the Movie, American Beauty. In this movie each of the characters have a similar or directly conflicting drive to the main character's and it's that drive that moves the story along. The main character has just realized he hasn't been living his life for him. He's just been going through the motions doing what you're "supposed to do". His wife embodies that exactly, a person going through the motions, doing what's expected of them and trying to find meaning in that. His daughter represents the youthful rebellion against this, she doesn't want to become her parents, lifeless shells of consumerism with no actual purpose. Her boyfriend, the neighbor across the street embodies what both she and the father want to be, a man who has found what he wants to do with his life, and is pursuing that. And lastly we have that boyfriend's father, he has been repressing who he really is for so long that he acts out violently, and provides the antagonist for the story. Through these similar motivations the characters are driven to interact and are able to tell a compelling story.
Applying that to a game is pretty easy, though, not every character in every story has to fit into this, sometimes they'll exist for another reason. For instance, lets look at Depraved Awakening, widely held up as one of the better story based games in our community. In it, you are a detective looking into the death of your client. Your supporting cast consists of the client's wife, her neighbor, the prostitute who was her friend, your step-daughter, and the patsy for the antagonists, of which there are a few who matter as well. Everyone but your step-daughter, fits into this narrative. Your step-daughter exists as your weakness, as the method by which the antagonists can get at you. Each of the other women, serve some role in the plot. The wife likely, inadvertently, caused the husbands death, though it also could have been related to the neighbor, who they were trying to help. The neighbor is linked into all this through her husband, an accountant who does the bidding of the antagonists. The ginger is working for the antagonists inadvertently, and due to some blackmail, is used by them to get to the MC. The hooker with a heart of gold is friends with the dead client and his wife, and so is willing to support you in your crusade. Everyone has a role to play, and each adds something to the plot.
Then we look at Man of the House, none of that is true. The premise exists merely as an excuse to show us a family fucking. The girls are all antagonists working against the MC getting laid who he has to conquer, they have very little motivation of their own, and what they do have is all contrived. Mom falls for the cock, the big sister has one of the worst blackmail plots and you flip a switch in her that makes her a willing sub in less than a week, and the little sister is innocent and taken advantage of. There's no motivation, there's no drive, they just exist to be fucked.