If you add up the various parts, then Penumbra: Black Plague ought to be a decent if unmemorable adventure game, however the developer has really nailed the elements of mystery, suspense, and isolation. You start to inhabit the character, which is apt as he himself is being inhabited and taken over by the titular plague. Little touches like the ambient music and subtle film grain only add to the unsettling atmosphere, which is utilised via various plot devices almost as a weapon against your senses. Definitely worth a look if you like those kind of bleak horror movies that make you sleep with the light on.
Mass Appeal: 7