Animations: I'm yet to see animations good enough in a porn game to justify the work put in them, I would take a few extra renders/drawings than one choppy animation.
Graphics: the thing I've been getting more and more frustrated with the current way of making porn games is the lack of energy and dynamic in the graphics. I read a lot of comics in my free time and I'm used to seeing people putting all action, emotion and charisma in still images, yet I look at porn games and see people standing with a blank expression and flat angles.
Of course, that presumes you will have graphics in a game and that's not completely necessary, there are good games out there without or with minimal visual content. That, of course, means the creator will have to compensate with writing and maybe mechanics to make up for the loss of visuals, but they are now unburdened by the limitations of what they can draw/render, games like CoC and TiTs would just not be possible if they had graphics (unless fenoxo had a fortune to spend).
Genre: there's no right and wrong regarding genres, all kinds of games have their worth and public, anything from your cookie cutter by the numbers VN to ultra-porn furry text based game. It's about what you want, need and can do.
Story: for me, a story needs to have a hook, something unique and interesting that no other game can offer. No need to follow trends or reject then, just build something to draw the player and keep them engaged.
And while I'm in the story department, the Main Character, I can't stress how important it is to get this person right, it's easy to forget and focus on the love interests and try to come up with new way to get lewds, but all is worthless if the player can't stand their protagonist or worse, are bored because the main character is a boner with legs. If anything, at this point with so many blank MCs (or so bland that they might as well be), I believe it's better for a creator to put more personality, flaws and backstory to their characters than make a player avatar for self inserts.
Choices: choices are nice when done right, even if they don't have long-standing impact, I like when I can feel the weight in the choices I make and see their consequences.
Multiple endings: much like choices, I like when they are done right, when they reflect and reinforce the overall story of the game and give liberty to the player one final big choice.