To be honest, I have mixed feelings about the upcoming Dante's Inferno:
It's made by a lot of the same guys who made Dead Space, now called Visceral Games, so I have little doubt that they're aiming for high quality and they have the skills and drive to achieve it. Actual gameplay hasn't been shown yet, but the general idea of melee action through monsters and areas fashioned after Dante's dream of Hell is definitely exciting. My guess is it's going to be pretty sweet.
But, though I'm sure the game will be creepy, Visceral seems to be inherently dampening fear of Dante's demons by making them all mortal. When you give a character power over a threat, that threat is less intimidating.
Of course, perception is everything. Perceived power is more important than actual power when trying to instill fear. A perfect example is the fight between Sam and Shelob, the giant spider, in LOTR: The Return of the King. It seems as though Sam is hopelessly outmatched, and that is what makes the encounter frightening.
If Sam immediately demonstrated some success, the scene would be less thrilling. If his success was predictable, if it was more the result of careful planning than of impulsive decisions and quick reflexes, we would fear less for Sam.
The biggest hurdle for a game designer trying to instill fear is certainty of victory. If a player knows he must defeat an enemy to progress in the game, then he immediately knows that victory is possible.
Books and movies have been killing off supernatural foes like demons and spirits for millennia. But I've always thought the ghostly tales predating the French Revolution and its cultural aftershocks are the better frights. Authors often played with the Christian understanding of demons, angels and souls; a perception that spirits could not be killed and human beings have no physical capacity to oppose them. People could only mentally resist and call upon God's effortless protection. Folktales preceding Christianity also involved struggles between humans and spirits in which humans used only their wits to escape, capture, or banish the spirits... rather than to destroy them.
Anyway, so here are some recommendations I would make to the Dante's Inferno team.
Don't make every enemy effectively mortal. Instead, provide non-lethal ways for the player to defeat the most terrifying beings. For example: a particular demon might be bound to a certain area, so the player could escape the demon by crossing some threshold (with that demon, and others, actively impeding progress and giving chase).
Satan in particular should not be killed. If it were my choice, I'd end the game by letting the player seemingly make headway in a battle against Satan, then proving the devil to be far superior in might and, in the end, apparently victorious. When the player seems defeated, that's when God reaches into Hell to deliver him. This ensures Satan, the game's final enemy, is as terrifying as possible. It also respects Dante Alighieri's belief, clearly represented in his tale, that he is saved by God and not himself. It would be a fresh game experience for most players. And finally, it could make for an exceptionally powerful story experience. In fact, I would have the player rescued by cherubs or children. In Christian theology (Dante's theology), the youngest and most innocent child could not be touched by Satan himself so long as God protects the child. That's a powerful image: a fearless, smiling young child ignores the demonic ruler of Hell as he or she takes the hand of the player's character and leads the player up a white stairway to Heaven.
For those epic enemies which are mortal, ensure the player must make use of more than strategy to win. Obviously, you don't want to stack the deck too heavily against the player, but ensure that the encounter retains some unpredictability even after the player gains an understanding of what that particular enemy's strengths and habits are.
Introduce "enemies" which can neither harm nor be harmed by the player. A malicious ghost beyond one's ability to affect is a frightening experience.
Remember that Satan is known as The Deceiver. Undermine the player's trust in dialog, in companions, and even in basic senses. For example: spiders might suddenly spill out from Dante's armor and crawl across his body, causing Dante to react in panic... and then the spiders are suddenly gone (they were just an illusion). Or a damned soul might rest still while calling out to the player in a pathetic tone with words of remorse and a plea for aid, then transform and attack the player if he gets too close.
Obviously, I could go on for days, so I'll stop here. :)