By skyforbes I'm not just talking about how in both games the player is stranded in an isolated area and needs to collect resources and eventually find a way to escape. There are many games like that. These two in particular feel so similar because of the way they combine exploration with narrative progression.
You get a nice open world that doesn't bestow many clues as to what's going on, just questions, at the surface of the playable area, but you find answers (and even more questions) the deeper you delve into the expansive cave systems underneath both maps. Of course, the biggest answers for both games being found at the lowest point in the map.
I think the biggest point in which these games differ is that Subnautica provides the player with a lot of help and waypoints on the HUD to find story locations, whereas The Forest provides very little help. The player basically needs to try every cave they see or may even need to consult the Wiki. But both games still provide progression through obtaining certain equipment that is required in order to go deeper (it's just a lot harder in The Forest without a wiki).
I won't specify too much, but both games also provide an incentive to work quickly and find answers (from a narrative standpoint, it doesn't really affect gameplay in either game).
Though, I wouldn't argue too much that they are both survival horror. The Forest definitely is, but Subnautica has only horror elements, I don't think many would consider it a horror game.
It's also not lost on me that both games entered early access the same year (2014) and were released in full the same year (2018).
Anyone else sort of notice this?