We should probably kick off this review with a public service announcement:

Consult your physician before playing this mod. Do not play this mod if you are pregnant, diabetic, or have a heart condition. Do not play this mod if you have any sort of nervous disorder, or are prone to panic. Do not play this mod if you are easily frustrated. Do not play this mod alone.

OK. On with the show!

Korsakovia is from the same gang that bought us Dear Esther, another HL2 mod that was not so much a game as an interactive voyage through a strange and surreal nightmare. This time round, the development team – who are, incidentally, a bunch of researchers from an English uni – have decided to give us a little more control, although we're still not sure if this is an entirely good thing.

The story, such as it is, follows the memories of Christopher. A thoroughly disturbed young man, we learn that he is suffering from Korsakoffs Syndrome – think Memento on steroids, acid and mescaline. With a tenuous grasp on his old memories, and unable to form new ones, Christopher fills in the blanks as best he can. As a result, we learn that he is convinced the world has come to an end. Despite this apparent apocalypse, order still reigns supreme, and any loose ends that remain (such as Christopher) are in the process of being tidied away by the “collectors.” These are Korsakovia's bad guys and they are utterly unique. Lacking any definable form, these malicious clumps of particle effects will hone in on you the second you enter their 360-degree line of sight, seething towards you with disconcerting haste. They are vulnerable to a thorough bashing with the crowbar, but more often than not you won't actually possess the good-old beating stick and will have to rely on pure adrenaline and the sprint button.

That the collectors can be killed is not immediately obvious, as the developers have stripped away many of the aural and visual clues that normally accompany combat. Even a killing blow makes no sound, and with no way to know if attacks are having any effect these brief periods of combat are surprisingly stressful. More stressful still is attempting to flee the gaseous rascals with no clear idea of where to proceed. The usual signposts to progression are all absent, and it's pretty much a case of trial and error as to where to go next. This can be frustrating, but when you're unarmed, disoriented and being chased by three pissed off cumulonimbus clouds it's flat-out terrifying. To further enhance the panic there is no health display, and the small cracks that slowly grow from the corners of the screen are the only clue to how much damage Christopher has sustained.

It should come as no surprise that these cues and clues are unreliable, given our protagonist's condition. While he is suffering from acute psychosis his physical condition only amplifies the weirdness of his “memories.” Christopher is blind and, true to the horror theme, it's not as a result of an unfortunate birth defect or macular degeneration, but an act of impressive self-harm. Having gouged out his own eyeballs, the doctors were unable to find the missing appartus and, for want of a better explanation, concluded he had most likely eaten them. Yummy.

As such, he isn't exactly the most reliable (eye) witness, and as the game progresses, his shaky grasp on reality stutters and falters to disturbing effect. While this is cleverly portrayed with some unsettling – and occasionally stomach-turning – visual effects, it's the sound that really ramps up the tension. Jessica Curry, who also made our ears weep in Dear Esther, returns here to freak the bejeesus out of us once again. It's clear she's been spending some quality time in some very dark places. The voice-acting is impressive, given the budget, but the haunting soundscape that accompanies the dialogue really sets the teeth on edge. Loud bursts of static, familiar yet unrecognisable sounds and slowly building (dis)chords invest the largely empty halls with an urgent tension that has a noticeable and immediate laxative effect.

While thechineseroom does a great job of creating a deeply unsettling universe, there are a few false steps that tarnish the overall experience. Platforming in the Half Life engine has always been horrid, and a few frustrating sections – particularly in the last couple of levels – simply shouldn't exist. The environment can come across as a little bland at times too, with more empty rooms than are entirely necessary. The lack of signposting can be a big impediment to progress, and lesser mortals have been known to resort to noclipping to find that craftily concealed ladder to carry them to yet more hallucinatory shenanigans elsewhere in the facility.

These are but small gripes in the grand scheme of things, and Korsakovia pulls off far more hits than misses. Given that the budget for the mod was a mere £10,500 we'd love to see what these boys are capable with Valve's development budget. Actually, considering how terrifying this budget effort is, maybe we’d rather not...

Ready to play the role of a man who thought it was a great idea to pluck his own eyeballs out? Don't say we didn't warn you.

1. You'll need to have Half Life 2, Episode 2 installed, with the latest patch.
2. Click here to download and install the full Korsakovia client
3. Turn out the lights, crank up the surround sound, put on your man diaper and get ready for a truly bizarre, truly creepy gaming experiment.