It doesn't seem like Faith: The Unholy Trinity should be able to do this, to scare us, because it looks like something I played decades ago on a BBC Micro. It's got squiggly MS Paint lines for graphics, there are maybe two frames of animation, the sound garbles anything it plays, and you can even hear system beeps. And yet, somehow, Faith manages it - manages to be unsettling, manages to make me jump, manages to scare me. Had I played this as a kid, I would never have slept again.
The theme is exorcism, and Faith begins with you, a priest, driving along a road and parking by a forest, then getting out and walking into the trees. You're going to finish what you started, with or without the Vatican's permission, you're told, and that's really all you know. Faith is a game that doesn't tell you much because working out what you're doing is part of it.
Mechanically, though, you can't do much: you can walk around and hold up a cross. And holding up the cross near certain objects seems to exorcise souls from them, and doing so produces a note. And notes are important. They are what fill in the story around you, detailing who you are, what you're doing, what you're looking for and why. And they'll give you clues about what you'll find when you get there, too, the answer to that one nearly always being "demons".