For me what I like most about the Rance games is not that they are good games despite the eroge, but that the eroge allows the story and characters to be more mature and adult than normal video games or anime can hit. Like, adults fuck. A lot. Sex is a big part of adult life, and affects how adults interact with each other all the time. But most of the time games and other media are not allowed to represent that part of adult life, so it's shallow and pantomine. Like, actually Shakespeare wrote a lot about sex, wrote characters that fuck and think and talk about sex, which is why Shakespeare is great.
I don't have a great example but think about Bird. He's a guy that can't get laid, can't keep a woman. I mean, yes, you can have a character like that in a GTA game or an anime, but only Rance games explore the real misery of being a loser like Bird. Ok, maybe Bird is a bad example...
I guess what I'm talking about is a scene like what happens to Crook during the Mula Test in Rance Quest Magnum (which is one of my favorite scenes in the entire series). Can another series like GTA do a side story about how depraved sex cults are? Sure. Are there anime and hentai about sex cults? Sure. But they don't linger on it, come to existentially incarnate it the way that Rance Quest does. Like, the best a GTA game can do is condemn sex cults or mock them, boo hoo people do bad things, as Jane wouls say "It's a Sick Sad World", but it's all so surface compared to what Rance Quest did with it. GTA can't do gangrape like Rance games do gangrape.
It's not just the sick depraved hentai stuff either, but how some characters like Lia, Shizuka, Pastel, etc... are written. The way that characters can do genuinely shameful things and be ashamed of themselves that you don't find in any other video game. How petty and self-absorbed people are.
Like, I've been playing a lot of games on PS5 this year, and yes there are "adult" games on PS5 like Cyberpunk 2077, Death Stranding, Yakuza 0, GTAV, etc... but they are still operating at a level that is cartoonish and childlish compared to the Rance games from Kichikuou Rance onwards.