I don't even think it necessarily feels like it's written for adults. It's just set in a fantasy world and commits to fully exploring what that means instead of using it as window dressing to pander. It's the exact reason I ended up loving Minotaur Hotel so much. Like I adore Adastra. I think its world-building is extremely interesting and everything to do with The Parents is cosmic horror in the best way. But it also has scenes where Amicus has sex with an ambassador to save the MC's life and you walk in thinking it's cheating but not before watching the whole scene play out. It's written for a specific audience, rather than written for the story it's trying to tell. (It does mostly work in context, so it's better than a lot in blending the pandering.) We haven't even started a relationship in Pervader and it's so much better for it.
I also think the more subtle expressions aren't a bad thing for this story. Especially with Jymsar needing to warm up to you. It works and helps make his arc feel special. It's more that it took multiple hours for Alen to get a second expression despite him having a plethora of them already done. If you're just starting it may give a false impression about how much work has been put into it. It stands out in scenes like the jail cell where it's talking about Alen being worried about your wounds and it's that static image of him smiling. Admittedly the side characters mostly only having a single expression is noticeable, but it's also a case of being understandable because the effort that would normally go into that has been spent on backgrounds instead, which is where Pervader truly stands out. Echo didn't add a lot of side character expressions until multiple years into its development, so that could always be done later as a finishing touch.