Groping to bed after an all-night session will make you wanna turn on all the lights you luckily find along the way.
The physics engine is quite impressive at first and this feeling holds throughout the game as you're being presented with ever more cunning uses of it. Opening drawers by really pulling them out, spinning rusty wheels on pipes, manipulating items freely (picking up, rotating in any direction, bringing them closer/further or simply throwing them away) or even smashing objects against each other gives a naturally immersive feedback. You know, the type of feedback when you got a nasty zombie on your heels, you rush the door in full speed, pushing desperately for it to open only to find out that it is opened the other way, which effectively means you have to step back or aside and actually pull in your (and your zombie friend's) direction.
Speaking of zombies, the designers used one especially nasty concept: you, cannot, fight, them. Splendid, isn't it? I mean, what can be worse for instilling and maintaining fear than the realisation, that you can't directly confront your enemy? In other games, after you massacre the scum who'd scared the hell out of you, you begin to feel somewhat confident. You just land a showy crowbar crack on its drooling mouth and then you can leisurely glower at its corpse, even loot it too, or piss on it for what it's worth - simply put, get to know and humiliate your enemy and shake the fear off.
In Penumbra, this is not the case though. You have to evade and dodge those buggers. Often just seeing them rounding a corner of an opposite corridor brings a strong urge to put to your heels as them bastards are fast and fairly sharp-sighted. And even though the stealth mode is done very nicely here, the safety of hiding in the shadows is rather dubious. When you find a good hiding place and watch the zombie for a while, the game switches in a panic sort of freak-out mode where your view gets blurry and zooms madly while you hear your character breathing jerkily in a strange psychic agony, which eventually leads to attracting the zombie's attention anyways.
Don't get me wrong though, you will have your satisfaction, albeit not that Rambo-style way of satisfaction. To be frank, later in the game, the dread factor kind of rubs off, you even discover ways to totally piss about the zombies, depends how cynical a player you are.
The story is fine, though most of its value comes from the fact, that you know nothing at the beginning and get to know only very little later on. Even so, it's mostly pretty expectable and when all's finally revealed with a great pomp, it shows several plot/design holes and brings a general feeling of "oh, well, That Virus Thing"... However, all in all it serves well.
Graphics and sounds are both excellent, considering the purpose of each - to make things generally... well, scary. Visually it is a bit dull, conforming to the overall spookiness, there's blood and rubble everywhere, which doesn't always make sense (especially in the toilet room areas, say what prook? ;), but there's a strange gritty quality to all of it so it simply works. Last time I remember being goose-bumpy-scared like this was in Vampire: The Masquerade, in that haunted house where the poltergeist kept on smashing pieces of furniture at you in the least expected moments.
The "puzzles" are great, more like real world obstacles, no nonsense. Together with the great mechanics, it makes the game for you. There's nothing in the world like rummaging around with a huge rotten mattress, trying to squeeze it into a small ventilation shaft and then climbing up there right behind it only to realize what an arse you were getting stuck in such a silly way. What with the solution being much more straightforward (and not involving mattresses in any way).