When Killer 7 first arrived at the OPS2 office, it came with a thick bundle of papers. The manual, pages explaining the game's background, a walkthrough and a letter that said: "Read the manual, it will really help" and ended with the plea "Give it a chance". Capcom, you understand, doesn't want its game misunderstood. It's easy to see why: the most coherent part of Killer 7's pot is the bit about the main characters (a wheelchair-bound man and his split personalities who come alive and kill monsters), the controls are unlike anything you've played, and it's one of the most visually distinctive games ever. But, despite its leftfield nature, there's nothing for Capcom to worry about, because Killer 7 is excellent.

The story goes like this: It's 2003, five years after world peace was declared. Underworld terrorist Kun Lan doesn't favour the new happy-clappy world and uses his mystical powers to turn people into zombified suicide bombers - called Heaven Smiles - that march up to their target, cackling as they explode. The US government doesn't like this (especially as Lan is trying to incite a war between them and Japan), so they enlist the help of his archenemy, deadly assassin Harman Smith. Problem is, he's old and stuck in a wheelchair. Oh, and he's also gone absolutely mad. Fortunately, this means that he's still lethal, as his fractured mind has created seven very different assassins that come to life and do his work for him. You play as the 'Killer 7', switching between them during play.

And as if having to keep an eye on more playable characters than there are cast members in ER wasn't bad enough, Killer 7's ace card is this: the controls are as mental as Harman.

Movement is conducted by holding down X - doing so propels your character forwards. Reach the end of a corridor or walk past a doorway and 'junction shards' pop up on the screen - you nudge the stick towards the relevant direction for the way you want to go. And that's just the moving around. To shoot up the Heaven Smiles, you switch to a static first-person mode by holding R1, tap the L1 scan button to make them visible (they're invisible otherwise) and then aim and fire using the left stick and X.

Complicating matters further is the gang's need for blood. Each Smile has a specific weak point, which appears as a glowing point on their body. Hit the weak spot and you're rewarded with a shower of blood particles, which you collect and use to top up health, power special attacks, or increase a personality's abilities. This is particularly important once you start battling the stronger Smiles found later, because it means you can level up your favourite character faster. Thankfully, that doesn't mean any neglected characters seem useless - a good thing considering you need every team member's abilities to crack the puzzles - turning Killer 7 into the kind of well-balanced ensemble piece that film and TV executives dream of creating.

But while it all sound elaborate in an instant migraine kind of way, it's actually simple in practice. The plot plays second fiddle to Harman and his mentally projected men - they're the stars of the show, and playing with them is as brilliantly engaging as it is initially confusing. Switching between personalities via the START button soon becomes second nature. In short: it works. True, if often works by virtue of the very fact that it is unusual, but it doesn't feel weird for weird's sake. You're never left resenting the fact that it is so unashamedly different and deliberately shallow.

Whether you're exploring areas or firing off shots as slowly advancing Smiles bear down on you, gameplay is remarkably tense for something so streamlined. Nerve-racking moments can be found around every corner, from outlandish boss encounters (such as the moment when two zombified politicians fire - get this - their own brains at you as ammo) through to incidental battles (check out the giant rolling Smiles, or the huge skyscraper-high Smiles that collapse on you if you get too close). The game has a great sense of drama, and the pacing rivals that of the best survival horror games.

It's with the pacing, however, that Killer 7 hits its one bump in the road - loading times. You'll often find yourself staring at a fuzzy blue screen of TV static (don't worry, that means it's the PS2 is 'thinking') when you move between areas, and as the off-the-wall puzzles require quite a bit of moving back and forth between areas, impatient players may feel frustrated. Luckily, players aren't stupidly lengthy, making the game's one significant frustration quite minimal, even if it does put a dent in the otherwise smooth pace.

But even with that one flaw, Killer 7 still excels on the basis of its presentation alone. Just look at the artwork and screenshots on these pages - there really is no other game like this. A lot of work has gone into making the images on screen truly unforgettable. When you switch personalities, the characters disappear and reform in an explosion of blood cell particles - and the same animation is used when enemies are successfully destroyed. Watching it happen never gets tiring. The environments, while stark at first glance, are actually filled with distinct detail and artistic flourishes, from a neon-splashed fairground to a burning Japanese restaurant. Hipsters will be referencing Killer 7's ultra-stylish visuals years from now, and the unique look is a huge reason why the game feels so engaging and special.

The sound FX excite as well. Smiles announce their presence with laughs ranging from a haunting giggle to the guttural chuckle of a demon perving off under your bed. The ghost characters are subtitled, talking in gargled or dreamy electronic tones - which sound most comparable to what would happen if you made Stephen Hawking's voice machine sing an Annie song while scuba diving. Music is hugely varied, with trance, Mexican, dance and orchestral themes playing at certain points. We'd go so far as to say that it rivals Metal Gear Solid 3: Snake Eater in terms of audio production.

It's also one of the first games to throw adult, edgier themes in without seeming crass and exploitative. Make no mistake, this isn't for the under 18s. It's scary, but isn't schlocky; it's grown up (characters often fire off four-letter expletives) but never juvenile.

Admittedly, this isn't the purchase for someone who likes their shooters straight up and on the blandly-rendered rocks. Killer 7 is a heady cocktail that contains various splashes from PS2's Platinum line-up (there are hints of Resident Evil, Time Crisis and even Devil May Cry) but also contains so many fresh ideas of its own that it's doubtful that anyone would dare copy it. The content is deliberate and uncompromising, creating something truly innovative, which has to be applauded. Admittedly, this makes for a game that can be unnecessarily confusing at times, and the loading times do slow things down, but even so Killer 7 is an astonishing once-in-a-gaming-lifetime-opportunity. You'd be a fool to miss out.

Killer 7 explained in our handy FAQ

So let me get this right - you don't play as one character, you play as seven?
Yes. And, er, no. You do play as the seven different assassins that make up the Killer 7 syndicate, but they are all parts of one personality - they live in the mind of our eighth man, wheelchair-bound codger, Harman. Think Jekyll and Hyde or Fight Club, but with an extra five voices jocketing for attention. And lots of gunplay.

Gunplay?
Yes. Harman and his personalities are armed to the teeth - check out their bios below for an explanation of what they can do. A good half of the game consists of you using their weapons in a first-person shooting gallery mode to take down oddball demonic enemies.

So what does the other half of the game consist of, then?
In many respects, it's an action adventure with a big emphasis on exploration and puzzle-solving while you try to foil a terrorist plot. But you don't use the stick to move the character around, you choose which direction to face and hold down X.

You just hold down a single button?!
It's not as odd as it sounds, actually. When you come to a corner, crossroads, or a fork in the road, directions appear on the screen - if you then nudge the stick in the corresponding direction, that's where you'll go. Oh and Triangle turns your character around 180 degrees. It's surprisingly streamlined and you quickly get used to it.

But if there's a terrorist plot, then surely it's like Splinter Cell?
Ha! Lord, no. Have you seen it? Look at the artwork. With the setting as far from the dark and murky corridors of power as possible, the plot's just as esoteric as the visuals. It's as if you've started watching a David Lynch movie halfway through. And in reverse.

Ah, right. So the story's a complete load of old arse, then?
Funnily enough, it's not. It gradually makes sense as the game goes on, with references to past events shaping your knowledge of what's going on. Think of it like Memento, but acted out by fluorescent tubes and anime characters. Sure, its literary pretensions are a little too lofty, but there's a clear villain in the form of Kun Lan and his legion of bomber zombies.

Hmm, I'm not sure. It sounds too pretentious. Surely I'll just lose track and give up?
Perhaps not, as you regularly encounter ghosts of former targets who pop up to dispense advice or special items. That doesn't mean they're any less logic-defying, though - one guy wears T-shirts emblazoned with slogans such as 'Sex Maniac', while a chap called Iwazaru dangles into shot dressed in a gimp outfit.

Sex maniacs? Gimp outfits? So it's a little perverted then?
Totally. There's another character called Samantha who acts as Harman's aide. Primarily, she helps you save the game. However, she's also utter filth - at one point you find her humping Harman's comatose body.

Okay, I'm sold. It certainly sounds interesting. But what if I don't like it?
Then take it back and trade it in for Barbie House Adventures, you big baby.

Graphics 90%
Stark but beautiful.

Sound 100%
Most extraordinary soundscape on PS2.

Gameplay 80%
A solid horror game with unusual wrapping.

Lifespan 80%
You'll follow the story straight to the end.

Overall 80%
One of the most ambitious games on PS2. It's unusual, but totally original and beautifully designed. Completely unforgettable.