Martin (Harvey) is a sweaty, pudgy security guard in a London parking garage, watching the original The Human Centipede on a loop while keeping a copious notebook about it. He lives with his shrieking-nag mum (Bridson) in a grotty flat, and is haunted by the abuse he suffered as a child. Surely his leering shrink (Hutchens) isn't helping. Eventually Martin gets up the nerve to attack a young couple, and now he's on his way to gathering 12 hostages that he can turn into the ultimate human centipede.

Martin doesn't say a word: he rolls his bulbous eyes, smacks his lips and groans with glee as he puts his vile plan in motion. He also clobbers his victims so frequently with a crowbar that it's amazing any of them remain alive. That may explain why none attempt to escape his warehouse torture chamber during the long stretches when he's out doing other things. On the other hand, they're able to muster the energy to moan loudly while creeping around on hands and knees after the centipede is assembled.

Six shoots this in black and white, which undercuts the violence but also feels like a contrived attempt to mimic Hitchcock's Psycho. Instead, it looks more like a cheesy comedy sketch. Harvey's performance is seriously nasty, and he's likely to get a lot of work as a drooling psychopath as a result, but everything about the character is so over-the-top that we never take him remotely seriously. He's vile but never actually scary.

But the real problem is that Six abandons his big ideas. This can be read as an exaggerated spoof of how some think nasty movies can trigger mentally unstable people into doing something horrible. Or it can also be seen as blackly funny exploration of the way child abuse creates monsters. These things actually draw out some laughter in the film's early section, but they are lost as the grotesque violence turns both extreme and increasingly pointless.

Alike (Oduye) is a boyish 17-year-old straight-A student whose parents Audrey and Arthur (Wayans and Parnell) worry because she's hanging out with her lesbian pal Laura (Walker) at a notorious girl bar. So Audrey forces her to befriend Bina (Davis), daughter of one of her friends, as an alternative. Still inexperienced in love and sex, Alike is resistant at first, but discovers common ground with Bina, embarking on a friendship that promises even more. But will Alike find herself and emerge from her shell, or will the world teach her a harsh lesson?

Expanding on her award-winning short, Rees draws us in with gorgeously textured photography and a strongly internalised approach to each scene. She beautifully captures the variety of Alike's experience, from nasty looks and comments in the streets to the quiet surprise of a first kiss. As the film progresses, we vividly feel Alike's nervousness over a possible romance, worries about acceptance and, most powerfully, her fear of her own inner longings. Where the story goes is sweet, shocking and ultimately moving.

The story is beautifully anchored in Oduye's sensitive, honest performance. And it's all the more remarkable since Oduye is in her early 30s, yet so believably capture Alike's teen physicality and deep yearning to express herself. Her interaction with Walker bristles with promise, while the scenes with Davis are charged with something much more exciting: first love. Parnell and especially Wayans feel almost cartoonish by comparison. And Wayans goes far over the top as the oppressively religious devotee who simply refuses to communicate with her "wayward" daughter.

This hints that the story comes from Rees' own life, as she seems to be revealing her anger at her own mother. And it's in Wayans' performance that the film comes undone. Unlike Mo'Nique's cruel mother in Precious, Wayans' Audrey is never completely believable, veering wildly from caring to pushy to cruel. And her histrionics threaten to derail Alike's hugely involving personal journey, which thankfully remains warm and witty even in the eye of the storm.

Fred (Meaney) returns home to Dublin but has nowhere to live, so he ends up sleeping in his car in a damp seaside parking lot. But his quiet idyll is disrupted by the arrival of the music-blasting, drug-smoking 21-year-old Cathal (Morgan), who also has nowhere else to go. Using the local swimming pool as a bath-house, the two begin to become friends. Even though he's always in trouble, Cathal's youthful antics help Fred rediscover some joy. And in the pool, Fred meets Jules (Ahlroth), a widowed Finnish music teacher who offers a possibility for the future.

The film has a relaxed, soulful vibe that holds our attention right through the meandering plot while promising that there are even more interesting things coming ahead (a prologue glimpse helps in this sense). The interaction is earthy and often jaggedly funny, as the writing, directing and acting all combine to let us see the characters' inner layers. There are constant glimpses that reveal key thoughts and emotions, as director Byrne keeps the tone charming and personal.

Meaney and Morgan make a lively odd couple, bouncing oof each other in blackly hilarious ways. Even though Cathal seems trapped in a spiral of crime and drug use, he has a lot to teach Fred about how to survive in today's society. Meanwhile, Fred is helping Cathal find a bit of self-worth. The two actors develop a wonderfully prickly chemistry, that lightly balances the comedy and drama. And Ahlroth effortlessly brings a different kind of energy into the mix.

Director Byrne and screenwriter Creagh have assembled an observant film that feels remarkably organic in the way the events unfold. Even when the plot churns to take some harrowing, melodramatic turns, scenes stay grounded in real life in a way that we can easily identify with. Especially with the world's economy the way it is at the moment, when almost anyone can suddenly find themselves in a desperate state. And how they respond to it makes all the difference.

Holly (Bianca) is a jaded high-class Sydney hooker who's ready to retire to her dream life in Paris. But she has one more three-some to do and, when a friend lets her down, she finds a young girl on the street to take her place. But 17-year-old Shay (Mangan-Lawrence) has only started streetwalking tonight, and when their trick turns into a murder scene, they end up on the run from a vicious thug (Phillips) and a corrupt cop (Docker), with only a nice-guy cabbie (Farren) to turn to for help.

The film oozes low-rent style, as director Hewitt shoots the grubby Kings Cross streets with glossy washes of colour and a vivid sense of both camaraderie and menace. Strangely, the sex scenes are the least interesting elements of the film. But when things start getting scary, we feel the tension even if there's not enough detail in the characters for us to really care about them. This world is so squalid that the few signs of decency almost catch us off guard.

Bianca and Mangan-Lawrence look great on-screen and are believable in fairly implausible roles. Over the course of this long, nasty night, Holly and Shay find it much more difficult than they expected to get out of or into the business, respectively. These are tough women, but in the film they're little more than symbols of degradation. And aside from the taxi driver (get it?), men are all scum.

As a result, the film's cautionary tone feels more than a little corny. Especially with a few wildly gratuitous sequences featuring full-on nudity (to throw us off the scent, the first naked person on screen is a man). And as the story progresses, and a briefcase of loot makes its appearance, we wonder if the script won't undermine its own moralising by making vice pay. Because they certainly seem to feel that these women deserve anything they can get.