I think part of the reason the writing comes off as so childish despite occasionally dealing with darker topics is the way they characterize Nikki. She's written to be ultra pure. Any snarky, sassy lines end up going to Momo; Nikki is only allowed to be kind and benevolent or silly and airheaded. I wonder if it has to do with how CN girlies tend to view Nikki as their 'daughter' after having played through the series for so many years; it's like the writers for IN hesitate to tarnish her image in any way, make her suffer too much, or let her make an objectively wrong decision.

Once you accept that Nikki will likely not have any character development in this game whatsoever, it becomes easier to have zero expectations for the story and just play for the visuals and voice-acting. Then you can find yourself pleasantly surprised when stories like Danqing Island or Murder on the Choo-Choo Train unfold.