I don't know if Penumbra's story, as great as it is (so far) would work as a "passive" one, like in a book.
In a written story, all that stuff that goes on in the player's head, would have to be written, otherwise it's just a series of events, not a story, and that wouldn'T be easy. you have to create the atmosphere of the game, without boring the reader with detailed descriptions.
Megatron - proving that guns DO kill people since 1984
It would probably be best to wait untill all three episodes have been beaten, then you will have a better jist of the story. But you would still need to write it very well so it dosn't just end up as a series of events.
The developers have the basic storyline, and the only thing that is needed is a skilled author to write the stuff around the story. It could be done, even to the point of being a bestseller if done very well.