There's one story I always tell about the first Amnesia. The most memorable monster I encountered in it was one that didn't exist. At all.

The game's atmosphere was so overpowering, its rules so murky, that in a well-lit pump room I became convinced that an invisible monster was in there with me. This hall was meant to be a break from the game's nauseating tension, and I was flattening myself against walls, jumping at every dripping pipe, solving the puzzle and then running as fast as possible away from absolutely nothing.

I'm sad to say I didn't invent any monsters in Amnesia's indirect sequel, A Machine for Pigs - co-developed by Dear Esther studio The Chinese Room - and the devil's in the details. Or rather, he isn't, this time around.

Mostly though, Frictional's tactile first-person horror is intact. Players once again find themselves in a sprawling, dingy complex with no idea who they are or what happened here. These are slippery questions that redouble themselves as you march through the dark, which is always growing larger, more horrible: "Who are you really? What is this place, really?"

A pig's orgasm lasts for 30 minutes, you know. (Spoilers!)

It's these large questions that drive you through A Machine for Pigs' six or so hours - and it's actually in its plot that it eclipses the first Amnesia. As terrifying and inventive as The Dark Descent was, it struggled to answer any players who were brave or detached enough to reach its final third, where the plot devolved into a porridge-y mixture of alchemy, cults, alternate dimensions and imperfect set-pieces.

Without wanting to spoil anything, A Machine for Pigs' tale of a slaughterhouse gone wrong offers a more refined narrative, more coherent themes and explains less in its final act, letting the story leave the tracks entirely and go sailing into the abyss - which feels entirely correct. There are failings in the storytelling; the game can hinge heavily on found diary scraps rather than environmental cues, but I can't bring myself to complain. A horror game with a passable plot running right the way through is one of the rarest things in gaming, and in places A Machine for Pigs' plot, imagery and ideas can feel succulent. I'm looking forward to meeting other people who've finished it, just so I can share my favourite mouthfuls of dialogue, my favourite dingy reveal.

Though, if I'm honest, the first thing I'd say to another escapee of the Machine for Pigs is nothing to do with the plot. It would have to be: "Did you find it less scary than the first Amnesia, too?"

And then, slightly sheepishly: "And... less interesting?"

Let's be clear. This is still a terrifying game. It's an exhausting journey through a good few miles of flickering lights, nasty surprises and Things that want to make mincemeat out of you. Most importantly of all, once again you're given no means to fight said Things, just a single lantern that attracts them. I know an awful lot of people who couldn't get past the first hour or two of Amnesia because it was too scary. If that was you, stay well away from A Machine for Pigs.

Whatever you think this game's secret is, by the way, you're wrong.

But no small amount of butchery has taken place here. Amnesia's feature list is an awful lot smaller in A Machine for Pigs. Gone is the need to maintain the oil in your lantern or hoard tinderboxes to light candles. You won't be hiding in any more cupboards, barricading doors or watching them get knocked down - and finally, and most disappointingly, The Dark Descent's sanity meter is gone. I always thought it was the single most exciting of Amnesia's ideas - that players were punished for looking directly at any of the monsters. It was a terrible thing to have to look away and cower, conjuring in you a terrible fear of the unknown, but it also made you pay attention to The Dark Descent's excellent sound design rather than its ageing engine.

It's natural for features to get chopped and changed with a sequel, but A Machine for Pigs offers almost nothing in return. It only ever has you sneaking past enemies and running away when you get spotted, which quickly taught me when enemies would show up by whether the room was (a) large and (b) packed with pillars to lean around.

The level design seems similarly reduced to a series of speed bumps. The puzzles and challenges The Dark Descent got from its physics engine are here cut back to rote tasks. This does have one advantage - I can remember my dark descending in The Dark Descent coming to a grinding halt on a few occasions when I got stumped at a miserably signposted puzzle - but it adds to the irony that A Machine for Pigs is a story of one man's impossible hubris that seems to wallow in the last game's tone and tech without chasing every part of the artistry.

A Machine for Pigs for pigs has three moments I think might be worth the entry price alone. Savour them! Later. When you've calmed down.

I don't mean to give you the impression I was tutting at my monitor throughout. I definitely wasn't. I was, same as the first Amnesia, mumbling swearwords like a career drunk and issuing my new flatmates with firm instructions not to open my door suddenly, because the chance they thought I was masturbating seemed less important than the very real threat of me pooping myself.

A Machine for Pigs performs the not inconsequential achievement of maintaining the soul of Amnesia. This is still a game that understands that real horror comes from disempowerment, and from the unseen, unknown and unexplained. A game that manages to breed powerful terror from winding corridors and empty rooms, never once relying on monster closets and only rarely on jump scares. And on the handful of occasions that A Machine for Pigs does try something a bit different, it's as amazing as anything in the first game.

And no, it's not quite as long as The Dark Descent, but that also means that it doesn't run out of steam in the same way. If you're an Amnesia fan, A Machine for Pigs will absolutely keep you fed. There's meat here, and it's rich, and tender. Just don't think too hard about where it came from, eh?