Playing through Dead Space is making me wonder whether or not it actually scared the shit out of people. Personally, I'm finding it very tense, atmospheric and creepy, but not downright horrific. Well, the gameplay I mean.
Some of the scariest moments I'm finding are listening to audio logs, and reading the text logs. For example, one of the logs fairly early on in the game lists the names of all the deceased crew members of the Ishimura. The list is exhaustive. Another such moment is in either Chapter 7 or 8, and you find an audio log for a Chief Engineering Officer that goes something like,
"This will be my last log. I've seen what they do to them.... to the bodies. I can't let that happen to me. At least if I have no limbs, I won't be able to kill anyone....
"One more."
For me, the scariest parts in Dead Space aren't the Necromorphs or the exploding vents, though they do contribute to the incredible atmosphere. The scariest parts are the ones that expose you to the desperation of the survivors. I'm only on Chapter 9, and I've already witnessed several suicides that have made try to help them.
I think one of the things the developers really nailed was the feeling of being alone and desperate. Finding people who are clutching body parts, or commiting suicide makes you completely useless. This is especially so, as the characters don't actually die until you reach a certain threshold. As such, I've found myself running toward them to try and put them out of their misery. It's an interesting moral choice that I hope they bring over to the second.