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.
Keys, keys, and more keys.
This game has no monsters, no horror, and a very linear puzzle-based gameplay. It's very unlike the others. Its main purpose is to finish up the story of the series and it does that fairly well, although it may still be up to your interpretation. The new things include a bunch of dialogue and some new places and puzzles to try.