Step into the Dark is built around limited visibility: you can only see a small area around you, so progress depends on remembering what you've already passed rather than seeing what's ahead.
That constraint does a lot of work. A space you've mapped feels safe; a space you haven't feels genuinely uncertain, which is a hard effect to achieve with better lighting.
Limited visibility. You see only a small area around you, so the game becomes about mapping and remembering rather than reacting.
It's atmospheric and tense rather than a jump-scare horror game.
Yes — it runs in the browser with nothing to install.