It's a double edged sword. On the one hand I appreciate the visuals (in any visual novel), they are after all the meat of a visual novel. Moving to the sex scenes in a rapid fashion is only a positive then. Yet it is also a visual novel, there should be some writing in it.
That makes adult visual novels a bit conflicting: you don't want to spend 30 minutes with a dick in your hand waiting to crank one out, reading through bullshit you don't care whilst horny. And yet by having characters with actual personalities (when not a faceless player-insert) and interesting interactions that the player can see or is a part of, they become so much more memorable. Of course, it's up to the devs and writers to decide the direction they want to take - porn or writing, or whatever else.
Some of the most memorable characters in adult games for me have been those with a lot of "non-adult" writing - writing that isn't purely sexual. Someone like Ember in CoC or Bess in TiTS are those that I always think of when playing those games. Well, Ember is more a tsundere dragon and I just can't help myself. Bess has great sex scenes and an intriguing story that the player is directly a part of. Of course, both the games are an acquired taste as they are purely text with very few images - comparing them to a VN is hardly fair. The point is, that the writing of those characters - whether that be their personality that extends into how they act in bed, or their story in and outside the bed - is what makes them, to me, memorable.
In the end, as I said earlier, I'm probably in the minority when considering AVNs. It's easier, more popular, and more profitable to make simple stories with plenty of hot scenes. And when I say simple stories, I don't mean to insult anyone's intelligence by saying they can't read or write detailed stories. My point being that if a player is looking to the game to jerk off, they won't care about the protagonists grocery list, they want to see the porn.
If I continue I'm just going to run (type?) in circles, retreading the same points. I'm just one of those freaks who appreciates porn with a plot.
/rant over: this is a porn/piracy forum, any kind of literary analysis can fuck off