In the puzzle oriented expansion Penumbra: Requiem long lost friends will return and aid Philip on his quest, but can they really be trusted? In the bizarre world of Penumbra: Requiem players will experience another psychological thrill on a level unheard of. This time telling what is real and what is not will be even harder and not always trusting your senses will be essential in order to survive.
It's marketed as a horror game, and expansion to Black Plague, however this is not a Penumbra game. It's an eerie puzzle game. The only real fear presented in this game is the paranoia you get simply from knowing it's supposed to be a horror. Other than that, you've just got a puzzle game with some very minor Penumbra story sprinkled in. And the bits of story actually ruin it, in my opinion.
The puzzle aspect however is pretty spectacular. Many puzzles leave you with a great feeling of accomplishment, and some even make you feel like a genius. They're well executed, pretty, and the atmosphere is wonderfully executed.
The story is negligible, and best if you just ignore it. Trust me. Pretend this game never happened in Penumbra canon.