Love is all and love is nothing. Alexander Zeldin's devised piece takes us into temporary accommodation and shows us a slice of life below the breadline. Set in the communal area of a council hostel, where those with nowhere to live wind up, it's an unblinking look at poverty; what it looks like, what it feels like, what it does to human beings. It's undeniably galling, the way hardship piles up on hardship until people buckle, but there's something fundamentally problematic about Zeldin's approach.

"This place is crap, Dad," says a huffy adolescent boy, iPad in hand – a fair assessment. There's one toilet, a kitchen and a couple of tables between four sets of residents. A family of four are crammed into one room. Next door, a middle-aged man and his ailing mother share a bed. A Sudanese woman walks by. A Syrian man moves in. All of them live more or less on top of each other, with no privacy to speak of and no space to themselves. Breakfast means wiping down someone else's mess. A quick pee entails waiting your turn.

Very little happens. Colin (Nick Holder) washes his mother's hair in the sink. Dean (Luke Clarke) cooks his family dinner – a packet of microwavable rice split four ways. There's a brief showdown over a red mug. What you see are trivial tensions between people: the frictions that come from cohabitating and the abrasions that result. When life's wound this tight, tiny tremors do great damage. They can make people snap.

In his last play Beyond Caring, Zeldin showed us a workplace; the precarious grind of zero-hour contracts. Love's a work play too – only the work involved is the task of surviving. Men return from the council office; eight hours spent queuing for a shrug and a system failure. Emma (Janet Etuk) tries to get the kids to school on time. Colin cares for his mum, clumsily but constantly. Hope drains away, bitterness rises – and, every so often, love forces through. It's a smile from a small girl to an elderly woman, a pirouette to raise a titter, a son jostling his mother with a joke. More often, there's shame and frustration and pain, and ever so slowly, notch by notch, Zeldin tautens the tension and brings conflicts to bear. It blames a broken system. It points the finger at politics.

Love is undeniably powerful, and such restraint takes huge talent – but it's all the more problematic for that. Zeldin's almost showily unshowy; it's impossible to ignore the skill of the actors or the craft of the writing. It's a paradox: the more credible the action, the more contrived it comes to feel and while Zeldin's aware of that – blending the seating into the staging, as if we intrude on their space, and referencing art in the action (tinny hold music and stock Vettriano prints) – acknowledging the problem doesn't solve it.

On it's own terms, Love doesn't surprise as Beyond Caring did; its human stories are that bit more generic and its characters, less complex. At base, they're all hoping the same hopes and, second time around, the hyper-realism isn't quite so disarming.

This isn't poverty porn – it's too honest and too earnest for that – but it sits oddly in context nonetheless. It's almost impossible not to see the set budget, the cast's wages, the ticket prices and programme costs in light of the lives being represented – and for what? To show us something that exists, to drive at social change. There's no metaphor here, just illustration. Stick a phone number at the bottom of the stage, and it's not art, but an appeal. That might be admirable, but is it effective – or is it merely cathartic?

At the end, Anna Calder-Marshall bends the fictional frame and, as the oldest resident, wades unsteadily through the audience. She needs our support and, on press night, a woman in the second row reached out sobbing. "I'm so sorry," she said. But to whom and for what? Is that all? Is it enough? Is that love? I'm not sure.

Love runs at the National Theatre until 10 January 2017.