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Science-fiction. Commonly including things like aliens, advanced technology, and settings of outer space or distant planets. 

Games which have short playtimes and can usually be completed in one sitting.

Games where the primary goal is keeping the player character alive under harsh circumstances such as dwindling resources or a hostile environment.

Focused on using its text, moreso than its visuals or audio, to tell the bulk of its story/plot. (Still can have great audio and visuals, though!)