Letters, books, scraps of paper and everything in between can add a lot to the player experience. If done correctly, it can provide the opportunity for the player to learn more about the world they inhabit, the characters within it, or even to supplement the existing story. However, when key elements of the story are buried within blocks of text, you run the risk of the player missing out on critical components of the game.
Take Amnesia, for example. This intense horror game hinges on the player reading in order to progress plot. And while, for the most part, it succeeds in creating digestible and intriguing text, there are moments in the game where you will find yourself face to face with a four page letter. For some players it will come naturally to sit and read through the narrative. However, when faced with this length of story, especially during an adrenaline-pumping game, many will either skim through the information or disregard it all together, missing key details about what is happening in the plot.