Absolutely agree on writing, i didnt mention it because it would be very hard (or impossible) to come up with a formula on what makes writing succesful. Aside from pointing out things that make it fail. At least i cant do it. So its hard to weigh how limiting it is for a project. Its neccesary , in theory anyone could come up with something good , in practice few can implement it well consistently. But in almost any game its possible to discover some core idea which came from inspiration and has potential. Somehow its always an afterthought for me because its not a glaring hurdle but something anyone can experiment with. On the other hand i cant start drawing stick figures in the hopes that some will turn out to be top smut.
I cant tell how big the interest is in getting competent coding, but I can tell if art and writing isnt competent then all those games dont really need advanced coding as a priority.
Looking into renpy sounds interesting though. I plan to do it at some point just in case. Maybe there is an opportunity to make something later even if for free.
Personally, I think the key factor is how well you can appeal to your audience's kinks and tastes.
The art has to be good enough that you can fap to it.
The writing doesn't have to be good like a book. It has to be good at getting you off. The story is secondary. As long as the sex scenes are good, you can have the stupidest story and it's totally cool. Just don't make the story boring or a slog to get through.
Good pacing is also important. Scenes need to be long enough that people have time to enjoy their kink, but not so long that they get bored. I think if you understand your audience's kinks really well, or if you share the kink and are able to write scenes that turn you on, that should help.
Using this game as an example. What are the core kinks? Futa, futa dom, and partner sharing. Almost everything else is optional. And to support those kinks, the art is 10/10 AMAZING. So even without dialogue, you could enjoy the sex scenes. Other games have extreme kinks where the art is mediocre but the writing is raunchy and hot.
This game ALSO has solid writing. There is no penalty for fucking all the futas. But you do get different scenes for your choices. And the scenes take time to explore the kink without going on for too long.
