Doom At 30: Siren is a great intro to the hellish world of Doom total conversions

There are as many Doom mods as there are stars in the sky: jillions of accursed celestial bodies orbiting the supermassive black hole that is id Software, each infested with its own local flavours of cacodemons and keycards and shotguns. I've played just a handful - certainly, far from enough to pronounce myself any kind of expert - but I do feel like I've played one of the best in the shape of Siren, a Doom II total conversion from Dithered Output, the first episode of which can be downloaded free from Itch.io.

The mod's overall vibe is encapsulated, I think, by the sentient vending machine you meet a short way in, just round the corner from a rec room that contains a disembodied head on tentacles, and down the corridor from a tiered canteen full of ghouls and unsympathetic men with shotguns. You ask the machine if it has any clue what's going on. It tells you that its job is to keep its mouth shut and dispense soda. Can I have a soda, then? "No."

Siren's setting is the Redark, a habitation prototype established by "The Corporation" beneath the surface of Mars. Nobody's heard from the Redark for decades, and your job is to get down there and find out what's what. Slight tangent: there is surely room in one of the many Wholesome Games showcases for a sci-fi shooter in which you're sent to a base that's dropped off comms and it turns out they did just have a busted transmitter, and you stop for tea (a gentle colour-matching minigame) and pass on some gossip about your mate from planet LV 426, who says she's just discovered an alien derelict. Sadly, there is nothing wholesome to uncover in the Redark. Instead you get an army of Combine-ish stormtroopers on the one hand, and a motley assortment of ravenous mutants on the other.

The mutants are really awful. They are not a fun time. The initial crop of zombies are easy enough to put down, but after that you get Imp equivalents that move like xenomorphs, scuttling across the ceiling when they're not hurling fireballs. Thankfully, you're pretty agile yourself, equipped with a Quake-esque jump and a mantling move.

The aforesaid heads on tentacles die quickly but are hard to spot against grimy metal panels and grates; some of them lurk in eggs that hatch at unpredictable intervals. Ammunition is plentiful throughout the Redark's opening areas but when you're backpedalling firing wildly at these hissing shadows, it's easy to run dry. There's also a creature that disguises itself as inanimate objects, a la the Mimic in Arkane's Prey. The game's gun-toting human opponents are less overwhelming, but they are equally hard to make out in their jet-black armour, and lethal in numbers. Later on, the game mischievously turns its usage of flat enemy sprites against you by having you fire down at monsters who, from that perspective, are just flickering lines in the air. Elsewhere, it spawns them in blind alcoves to catch you out while you're retracing your steps. Nasty.

Then there's the titular Siren. I don't want to give too much away about the Siren, but suffice to say that if you hear the scratching of a thousand insect claws on the other side of a door, you should avoid opening it, and if you see smoke at the far end of a corridor, you should run. There are ways of dealing with the Siren, but so far, they don't involve bullets. Fortunately, the entity is as much of a threat to certain other denizens of the Redark as the player.

If the hazards are a handful, Siren's major hook is the setting itself. I realise that's what critics always say about sci-fi horror games in the Alien tradition, so let's be slightly more specific: the Redark is both a convincingly wrought and storied environment, and an interesting cross-section of FPS influences. There's the classic Doom loop of finding keycards and secret areas, but the layouts and interior design also evoke Dead Space in forming a coherent workplace, made up of areas such as loading bays, fuel storage and control centres with terminals that bestow hints.

The maps are impressively labyrinthine: routes launch you off to the map periphery only to deposit you neatly back at the centre, with a fresh wave of enemies to deal with. There's always uncertainty about where to go, but not so much that you feel stumped. There are also some great setpieces: a corridor with ribbed lighting that is deceptively quiet, until you rouse the robot sentry at the far end.

The aesthetics blend the original Doom's gunky pixels with latter-day flourishes such as CCTV displays that point you towards a new discovery in a previously visited area. The weapons, including pistols, shotguns and pulse rifles, are beautiful creations with similar modern touches. You can aim down the sights - the rifle has a holo visor, though I find it too unwieldy to use - and when you reload, you hear the discarded clip rattle across the floor, which is one of those disposable grace notes that somehow pins the whole experience together.

Siren isn't one of your fancy avant garde mods, like Sky May Be. It's just a very well-put-together horror shooter that both celebrates a 30-year-old FPS template, and grafts ideas onto it from successor titles and broader works of sci-fi. Mind you, it does have the capacity to get weirder. The incidental writing puts me a little in mind of Signalis, in that there's clearly some larger philosophical conceit at stake. I'm hoping that the Redark's lower levels will house twists and revelations that carry Siren beyond its debts to Scott and Giger.

For the moment, the first episode is a great introduction to the wider world of Doom total conversions, demonstrating both why Doom has aged so well and how much it can be altered while still being basically Doom. There's no 1.0 release date yet, but if recent triple-A haunted spacehouse escapades have left you cold, Siren's first maps could be what you're hungering for this yuletide.