The WP page has spoilers, but the intro gives the basic appeal:
The game does not follow traditional video game conventions, as it involves minimal interaction from the player and does not require choices to be made nor tasks to be completed. It instead places focus on its story, which is told through a fragmented, epistolary narrative as the player explores an unnamed island in the Hebrides.
I paid enough to get all of the other games as Proteus looks interesting.
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