Been thinking about this since I've been playing Rain World. I feel that Rain World is solidly within the genre. There are definitely video essays out there about it being about existing in an ecosystem or whatever. Pathologic is another obvious one. The original Dark Souls is probably paradigmatic of this category.
What traits define this category? I think:
- Difficult, you struggle to make progress
- Inscrutable narrative motivation
- Hidden depth to the world that can be teased out through intensive study
- Possible to find it fun, but much likelier to just bounce off (and watch the video essay instead!)
Is this a valid category?
Funnily enough, competitive fighting games such as Smash Bros, Tekken, and so on, are very prone to having 1h essays about the influence of a particular move in the history of the game's competitive playing. Or Tetris.