Four arms: it was so obvious. It must be galling for other shooter developers. They've spent decades since Doom trying to work out ways to innovate on the FPS model, to make shooting people feel fresh and interesting again. They've tried vast open worlds and they've tried hurling Hollywood-size production values at projects, but the Darkness II manages it by just giving anti-hero Jackie Estacado four arms.

Well. Technically he only has two arms. These are his normal limbs, functioning as arms do in games where arms are only necessary to hold guns and occasionally fire them at swarms of enemies. He also has two demonic snake-tentacles.

In the last Darkness game – an under-reported and enjoyable shooter sadly not released on PC – Jackie Estacado became the host for the titular 'Darkness', an eternally chaotic non-corporeal beastie that gladly took up residence in the young mobster's brainpan. The Darkness, it's understood, is about as old as humanity itself, every so often choosing a new host with just the right balance of psychotic amorality and poignant backstory.

In game terms, it means Jackie grows two pitch-black snakes out of his shoulders that can be employed in firefights to munch on the vital organs of his enemies.

At first, the four arms feel cumbersome. Jackie can already dual-wield all but the bulkiest shotguns and assault rifles, and The Darkness II's guns by themselves make for a satisfying shooter. Even the weediest pistol has a powerful kick, and they're almost comedically accurate over distance, lending Jackie a sense of overwhelming power that is consistently fun to direct toward your foes. But couple that with the option to whip the Darkness's serpentine limbs into scuffles, and it seems too much to fit around one WASD-ing hand.

But a few murders in, and I was surprised at just how quickly I'd managed to process the additional moves the limb graft gave me. Simplest of these is the Darkness's ability to eat the hearts of fallen opponents, available with a tap of the R key. The leftmost snake-tentacle – the busier of the two throughout the game – whips forward and buries its improbably huge teeth in the chests of mutilated enemies. Scarfing down such man-offal gives Jackie a health boost, making the decision to chow down on a mid-fight snack tactical. At first, I'd eat my foe's heart the second he slumped to the ground; later, as fights got tougher, I saved them, only launching my monstrosity chestwards when I was close to death.

Heart-eating might be the Darkness's simplest move, but impressively, it's not the ickiest. Jackie also has a variety of execution moves he's able to perform on staggered enemies. Throw a target off balance with a withering enough attack and they'll stumble forward, their hearts and circulatory system picked out through their skin in shining white. Tap E and your tentacle friend will grab them, dangling them just in Jackie's eyeshot, from where they can be eviscerated in a number of fascinatingly gruesome ways.

To get a flavour of just how depraved some of these executions are, the most dignified is called 'torso smash' and has your inkyblack snake pal slam your chosen target so hard into the ground that his ribcage ruptures. At the other end of the taste spectrum is the sickening move that has the Darkness upend an enemy and delve into their rectum, before pulling their entire spine – skull attached – out of the expanded hole.

Jackie's demon-arms can also be employed as impromptu whips: holding the middle-mouse button and slashing sends a high-speed swipe across the screen. I used this skill least, however: it's useful to clear a glut of foes crowded in front of you, but the default control method makes it a touch fiddly.

The Darkness makes Jackie superhuman, but it's not a 'win-all' button. Jackie can only employ the Darkness, fittingly, when he's in the dark. Lights banish the snakes from his shoulders with a shudder and a hiss. So too does Jackie's 'darkling' disappear, a three-foot goblin-like sidekick that somehow manages to stay endearing despite cracking wise for the length of the game and urinating on enemy corpses.

The lighting problem necessitates a systematic elimination of illumination: lightbulbs are the first thing to go after I enter a room. With the room submerged in gloom, I am free to rampage effectively, Jackie's full range of abilities at your finger and tentacle tips. Some later lights are invulnerable to gunfire, forcing you to find their power supply. Later again, enemies start to carry portable arclamps, cutting off parts of the battlefield with sweeping beams of horrible brightness and making a chap consider his surroundings carefully before launching assaults.

A successful series of kills rewards Jackie with essence – a wooshy purple substance that can be traded for extra powers. Some of these powers are functional, providing additional ammunition or shortening reload times; others are ridiculous. My favourite gave me the chance to hurl my darkling at chosen foes. I'd grab him before a fight, letting him hang off to the side of the screen in swimming pool 'cannonball' pose, before launching him forward, his tiny claws raking and scraping at enemy eyes.

The hyper-violence of The Darkness II is comic in the extreme – in both senses of the word. The game is based on the comic books of the same name, and its characters are, as befitting the title, black and white in morality.

After his escapades in the previous game – neatly summed up by an optional 'previously on The Darkness' cutscene – Jackie starts The Darkness II as the head of a mafia family, under attack from sources that want his power. He's obviously a violent man, having killed his first victim, according to cinematics, at 16, but he's given salvation through his relationship with girlfriend Jenny. One small problem: she was killed by a rival mob boss in the previous game. Without her physical presence, Jackie's moral checks are loosened, but even so the game is careful to steer him so the people in his way are unquestionably more disgusting and evil than he is. Jenny's death serves as a girlfriendshaped carrot on a stick, driving Jackie forward.

The Darkness II's enemies are so unquestionably nefarious that I rarely had time to stop and question the linearity of the levels. Your main antagonist has a hunchback, a limp, and a burned-up face, for God's sake: if he's not comic book evil, I don't know what is.

On the friendlier side, Jackie has a supporting cast of mobsters to help in his quest for vengeance. Between missions, you're sent back to the Estacado homestead, a plush apartment in central New York. These sections serve to add character to the gang Jackie is acting head of, but they could do with being a touch more interactive: after trudging around the grounds I was rewarded with one bottle-shooting minigame and a few incidental conversations.

That story can't keep up the pace forever. The final levels are a slog where their predecessors were a sprint, and the procession of maniacally grisly deaths eventually dulls the shock receptors. But developers Digital Extremes have orchestrated some careful pacing: the plot's headlong rush – 'chase them, find him, kill others' – has occasional moments of uneasy calm so interesting I won't spoil them. These moments of clear air serve to highlight the ferocity of Jackie's cleaving path, putting him in situations he can't shoot, slash or chew his way out of.

There are acceptable outs for players wholly unengaged with the story – cutscenes and dialogue can be skipped – but the plot remains involving in a way rarely seen in shooters. Again, I'm dancing around my words to avoid giant spoilers, but The Darkness II plays with concepts of unreliable narration in a way that only games allow. It makes you question the veracity of the story you've just played.

Also, it lets you pull peoples' guts out of their bum with giant demonsnake arms. The Darkness II is a dumb shooter that's three times as clever as it looks. So too is Jackie's murderous repertoire three times as extensive as that of other shooters. It might not last long and the action doesn't alter its tone, but The Darkness II's charms stuck with me long after I turned out the light.