There's more. Because something is less scary once you understand it, many of the monsters are unknown quantities. They frequently appear and disappear when you're not looking. You never quite learn the limits of their vision. You can distract them by throwing things to create noises elsewhere, but it doesn't always work. And while monsters are relatively rare in Amnesia, which saves them from ever becoming irritating in the way they would if the entire game was built around them, the game does a great job of making you feel that any of them could appear at any time. In one room I spent 10 minutes nervously sprinting from safe place to safe place to avoid a monster, except there was no monster. I'd only convinced myself there was.
There's more still. While monsters make for almost all of Amnesia's high drama, some extra moment-to-moment tension is added by your character's aversion to darkness.
Amnesia's Daniel is a card short of a full deck. He's brave, resourceful and smart, too, but also distinctly unhinged. Leave him in the dark (like you often have to do to avoid monsters) and his sanity drains. If Daniel's sanity drops too low he'll start to slow down and gibber to himself, and you'll get some serious lag on your mouse-looking and a hazy Vaseline sheen applied to the screen.
Your enemies against the darkness are tinderboxes, which allow you to light candles, fires and torches, and your lamp. But both tinderboxes and lamp oil are in short supply.
Again, that might sound annoying, but Frictional has executed it almost perfectly. The times when you get annoyed with this system are outweighed by the relentless atmosphere of danger it creates, with you fretting over your supplies and wondering whether to light that torch and lose another hiding place. At the end of my game I realised the prudence in flicking the lamp on and off to conserve oil, which actually results in a flicker-cam straight out of any horror movie.
Amnesia's problems are all to be found outside the horror. It's relatively short, clocking in at about eight hours, but since it's being sold for $20 ($18 if you pre-order) I wouldn't say that's an issue. What I would say is an issue is the plot's resolution, since Amnesia does mystery better than it does concrete answers, some of the voice acting, the odd bit of uninspired level design and lots of the puzzles being too simple to involve any thinking.
Amnesia's overwhelming confidence and competence as a horror game takes it so, so close to being excellent, but there's just not enough content. The horror peaks whenever you're forced to deal with some new, unknown element, and those situations can be counted on the fingers of one hand. It's more than just a missed opportunity - by the final third of the game, as you reach the true heart of the castle's darkness, the monsters start losing their mystique and becoming 3D models.
Still, fans of horror gaming should definitely have Amnesia: The Dark Descent in their lives. It's a brave experiment in the genre, a more solid package than the Penumbra games and stops at nothing to make you truly, deeply uncomfortable. And after a hard day at school or the office, isn't that all we really want?
Amnesia: The Dark Descent is available to download for PC, Mac OS X and Linux from tomorrow.