I just downloaded the demo of this and found it to be the most frightening game I've ever played. It's just the sheer feeling of helplessness that you get when you're being chased that caused me to frequently empty my bladder when I played it.
Here's a quick summary-
You play Daniel, a young man who has just awoken with amnesia in a massive labyrinth of a castle. When you first wake up, there's splats of some sort of drink and a strange PANK substance on the ground.
As you follow the trail of fluids you see a whole lot of nothing, but are guaranteed to shit yourself when doors randomly open around you in barely lit rooms.
Speaking of barely lit- light is a major dynamic in the game. To quote one reviewer, it's "Guaranteed to reinstate your childhood fear of the dark." Which it did to me almost immediately after the start, utterly decimating any comforting reassurance that there was nothing out there that was going to eat me by taunting me with screams and screen-bending effects.
Much like the penumbra games from the same developer, another major factor of the game is insanity, which will increase from specific events such as looking at the "shadow" (the monstrosities that chase you, they "slowly destroy reality" and are gradually converting the castle into some horrifying hellhole. If you catch a glimpse of it, look away and get the fuck out of there, otherwise it will see you and kill you.) You also become more insane if you sit in the dark, so you have to collect timbers to light candles and use your lantern sparingly as it has a very limited amount of oil.
There's only one objective in the game that I've seen so far- to kill an old man who resides within the inner sanctuary of the castle, which is undoubtedly another test of your own strength of mind.
I have yet to determine how you're supposed to kill said old man, as there are ABSOLUTELY NO WEAPONS to speak of within the game. Your only way to survive against the beasts is to barricade doors while you hide from them and run like hell.
There's a really cool dynamic I've seen in the game, though. When you pick up objects, you can pull them closer or push them further away from you, as well as throw or just move them. All of the doors and objects within the game work on the same principle- if you grab and move your mouse, it will move accordingly. For that reason, you have total control over how a door opens or closes, if it moves quickly or slowly, and how open it actually is. You can also push objects that you can't pick up, and it makes you really feel the resistance of their weight as you do.
TL;DR: Enthralling game, good graphics, good physics, play it- piss yourself.
EDIT- Whoops, left out the teaser:
http://www.youtube.com/watch?v=M627-obxNzg