Idea: Hardcore Amnesia

[turk]

You can always increase the cost of failure and the likelyhood of it without increasing the number of beasties and such. Simply tuning it to require quicker reactions would increase the amount of stress on a player considerably. To have to be able to react within a split second or die is incredibly stressful (and if done poorly potentially incredibly frustrating) for extended periods of non-activity. The more arbitrary something is as well the more difficult it becomes. Take this into consideration also.

False danger is one route you could take, pressuring the player into real danger. Or real danger pressuring the player into false (yet seemingly real) danger. To mix instances of expected (yet non-existent) failure and actual failure appropriately and arbitrarily enough creates indecision and difficulty.

Simply removing light from the beginning also would probably result in lesser results (I believe) than removing it when the player would typically require it, creating pressure to play defensively (hence difficulty) because of inherent unpredictability. That light you planned to use, is now gone, so you'd better hope you have a backup plan.

EDIT: Another thought perhaps would be to alter the door mechanic. Stuck doors that require shaking could be very frightening as you may spend 5 seconds shaking a door to try and knock it open only to find that it simply wont budge. At the same time you could do it and find that it does, providing your much needed respite.

Reducing the vision and audio would also make the game more difficult (and possibly frigtening) as you would be running around virtually blind. Simply reducing the overt signs of danger is a way to increase difficulty.