It is difficulty to try and write about Amnesia: The Dark Descent in a way that does justice to the game, as any kind of detailed recommendation cannot help but to defeat its own purpose. The game's appeal is all about mystery and the fear of the unknown. This article does its best to avoid heavy story spoilers, but analysis by definition is the very antithesis of both, and if you actually care about immersion and the power unfamiliarity, the experience will be the better the earlier you quit reading this article (or any kind of review) and start playing the game already. I'd even go as far as recommending to disable the ingame tutorials; the mechanics are not that complicated.
Amnesia begins with the protagonist waking up inside a dusty old castle, barely clinging to the memory of his own name - Daniel. Following a strange trail of purple freckles through the darkness, he soon stumbles upon a letter written by himself, telling him he drank an amnesia-inflicting potion to forget certain incidents, and one dreadful instruction: Find and murder an old man named Alexander of Brennenburg in the castle's Inner Sanctum.
The entire game is played through Daniel's eyes as he makes his way through the murky ruins, finding pieces of his own diary and other documents along the way, which reveal one by one the horrors that happened before the fateful drink of oblivion. Sometimes Daniel also gets visions of the past when he crosses locations that used to be familiar to him. The player remains in control during those, but the sight typically gets so bad that it's not feasible to do anything that goes beyond continuing to walk down a straight corridor. Like in the System Shock and Bioshock series, pretty much all of the narrative happened before the game, and it's left to the player to unearth the records of what happened. One by one, the notes reveal a truly bleak view into ancient horrors as well as the darkest voids of the human soul, and the fact that the majority of it is written by the player avatar himself makes the narrative feel all the more direct and "close to home."
Most of the castle is shrouded in darkness, but one gets an immediate sense that the shadows are not good for your health - when staying in unlit areas for too long, your senses get twisted, you start hearing noises and hallucinate about what may lie in the shadows. Compared to a game like Eternal Darkness, however, the "sanity effects" are rather subtle, no fourth-wall breaking stuff here. The game does a very great simulation of the need to adjust your eyes to the surroundings for a few seconds after diving into the darkness, too. Throughout the castle, Daniel finds tinderboxes that enable him to light candles and torches to drive out the darkness. He also gets a mobile light source in form of a lantern, but it has to be fueled with oil regularly.
Amnesia manages to instill a fear of the darkness into the player without throwing in any kind of horrible monster or obvious immediate threat for hours. Early on, players will find themselves clinging to brooms and chairs to arm themselves against the dangers that might lurk in the unknown. And as soon as one gets over the fear of the darkness, the game draws attention to other menacing uncertainties, like murky water. Eventually it even drives you to seek out the darkness, as it eventually turns out the only protection against greater evils. The castle also soon starts to get infected by an unhealthy-looking red taint, that actually hurts Daniel and obstructs his progress. On the other hand it takes its due time to introduce its monstrosities; at first you'll just see shadows scuffling through dark corridors from afar, and for a long time it is everything but clear whether or not they're just products of the protagonist's imagination. When they finally strike, however, they strike fiercely, and carry more potential to inflict terror than all the creatures of Raccoon City and Silent Hill combined. The atmosphere in the castle is truly phenomenal, and the crawling bugs and other gross-out moments are genuinely disgusting.
Amnesia: The Dark Descent
As a kind of Immersive Simulation, Amnesia has no on-screen display whatsoever, but there is an inventory screen where it's possible to check up on Daniel's health and sanity, and to manage items that have been picked up on the way. Only certain items can be carried around indefinitely, while most objects are only held temporarily in front of the player's eyes, where they can be carried around, rotated or thrown, as Amnesia uses the Havok physics engine for them.
About half of the puzzles in Amnesia are thus physics-based: Throw a rock to destroy a chain, put the cogwheels of a machine together so that they fit, or pull a bed from over a trapdoor. The other half are typical inventory puzzles, where items are combined in the inventory and applied to objects in the 3D view. Compared to the rest of the game, they're all pretty standard survival horror fare and fairly simple to solve, but at least here they all fit in with the scenario; as one descends into the lair of a mighty and mad alchemist, all the weird contraptions and rituals are to be expected.
Amnesia is not without flaws, though; its humble indie origin is betrayed by the limitation of its assets. The focus on atmosphere instead of fidelity is laudable, but at certain points the lack of variety can be quite the immersion-killer, for example when one recognizes that Alexander was apparently the author of a book called Pflanzenreich ("Plant Realm"), and it failed horribly at retail - how else is it to be explained that he keeps several hundred copies of the work? The physics engine also quickly shows its limitations, and the distinction between what is grab-able and what is not often feels arbitrary. It's stupid fun to pull all the books out of a shelf to throw them at the floor, but when moving on to the next shelf one has to discover that all the books are apparently glued to it.
The worst problem of Amnesia has nothing to do with its budget, though; and that is the utter lack of penalty for dying. When killed, Daniel just starts out at the beginning of the current (small) map, even keeping all collected items. Therefore it's not much of an issue that health becomes pretty much pointless in the latter half, when everything that's a serious threat is capable of killing him instantly, but that's not for the better. Forcing the player to start large parts of the game all over, or making the game even harder are devices that have been rightly discredited as inappropriate means to punish failure, but game designers have yet to come up with a meaningful way to replace them. In a genuine horror game, solving this problem is even more important than anywhere else: The suspension in Amnesia takes a severe hit as soon as one discovers the complete absence of "real" danger. Resource management also loses its bite in the second half of the game. In the beginning it's often necessary to spare light sources, but once one has figured out when and how to best conserve them, Daniel quickly ends up with a very healthy stock of tinderboxes and a reserve of spare oil for the lamp. In a way Amnesia lasts too long for its own good, even though the official story takes less than ten hours to complete (there's also the option to load custom-made mods, of which there's quite a few available).
Amnesia is still a very intense experience at least in the first half, and overall one of the most frightening and unsettling games ever. Especially the extremely morbid references to torture are not for the faint of heart, even if none of it actually happens on screen. Big budget survival horror may be well underway of having abolished itself, but indie games like Amnesia prove that there is still a future for the genre.