It depends on the game....but I like to see some of the story/characters (and like others said with real background.....without the background the girls are just dolls) and some sex scenes. It doesn't have to be a lot, but imo there should be some, for at least a couple of reasons:
1- Slow burners are fine, but I want to see whether the XXX content can be worth the wait.....some devs might just never add that content or add poor content....so I'd be like, what? I waited months for this? No, imo a dev who's not showing much either isn't serious about making an NSFW game or could be a scammer.
2- I hate and despise H games that have tons of grind/silly dialogues/pseudo writing and very little in the way of content.....
I agree with other posters: I need an interesting story or interesting characters (otherwise I could have watched normal porn), but let's be honest, those are rare. More importantly, grinding mechanics and endless dialogues meant to be funny (but in reality just meh, or the kind of silliness anybody could write) do not make anything interesting, imo, they are just tools employed to disguise a fundamental lack of anything interesting to say....and to waste the player's time.
I'm in pre-development with a game of my own (still creating a fictional version of the future, filling a notebook with maps, lore for different races, characters, main plot, possible side-stories etc)
It's an ambitious project but I will eventually produce a short demo and see what the response is...if there is interest I'd love to continue and complete the game, if not I will use the plots I have for a novel (maybe erotica, maybe just a techno-fantasy thriller). I have a good plot, imo, and a very interesting, detailed setting. I wouldn't want to waste them.
Anyways, next I plan to produce a brief trailer (for a few glimpses of my fictional future, finished the script for that one yesterday)
and of course the demo.
Since my game aims to be a combination of a VN and a sandbox trainer/dating game (with relationships that can lean more toward romance or domination depending on the player's choices) I want to create a demo, regardless of how long it takes, that contains the beginnings of the overarcing saga but also the option to have fun with the first girl/girls to join the MC's harem, and maybe to have some lesbian sex since that will also be big part of the game moving foward.
Obviously I'm not going to try to cram every fetish and character in a short demo, but yeah, I want to create something that at least showcases all the main elements.