Compared to the glitz of Cannes or Sundance, the documentary film festival tends to be a more earnest beast. There are rarely superstars posing for paparazzi, or headline-taunting auteurs defending their misogynistic directorial choices. The “stars” are directors who have chosen the less travelled route to moderate fame, and the post-film Q&As often feature characters whose lives the audience has just seen put through the mill for 90 minutes. This makes for an odd but energising mix of polite respect and leftfield critiques of real people’s lifestyle choices.

Next month sees the launch of the 25th Sheffield Doc/Fest (7-12 June), the UK’s most high-profile showcase of documentaries new and old. The city is the perfect place for such an event, the festival reflecting Sheffield’s singular mix of leftwing politics, radical art and an outward-looking bloodymindedness.

This blend sums up the current state of documentary film well. At the world’s largest documentary festival, IDFA in Amsterdam (in November), there tends to be a creative tension between the advocacy-led journalistic social issue film and the more lyrical, slow-moving authored pieces. Post-film discussions can be explosive, with earnest daytime cinema visitors lecturing film-makers on their political or aesthetic woes.

Meanwhile, Copenhagen’s CPH:Dox, which takes place in March, is all about the border country between fact and fiction, especially where the film-makers are artists too, frequently leading to viewing experiences that are bewildering and uncomfortable. This is usually a good thing, with large, hip young audiences coming to be provoked.

Often it’s outside the cinemas that the really intriguing things happen. Most festivals feature discussions on the state of documentary commissioning, and round-table pitching forums. These offer a chance to take funders to task for their love of safe or exploitative commissioning decisions. Sheffield does this particularly well. Even in its highest echelons, the documentary industry is a comparatively accessible cottage, one where decision-makers are held publicly accountable by audiences and peers alike in an enjoyable, if sometimes cringeworthy, style. But at the end of the day everyone drinks and dances together, because in documentary if you’ve got airs and graces you probably won’t prosper.

In this vein, Sheffield’s identity is increasingly one of hearing from less exposed voices. Its 2018 programme opens on 7 June with the world premiere of A Northern Soul by the Hull-born Sean McAllister, in which he deconstructs the hype around Hull’s year as 2017 UK city of culture. McAllister makes films that tell an authentic story of global working-class experience, where art and grit are not mutually exclusive and we see depths to people frequently dismissed by media outlets as only good for news bulletin voxpops.

RaMell Ross’s magical Hale County, This Morning, This Evening takes a microscope to the daily routines of an African American community in Alabama. This isn’t a film about racial discrimination or struggle, it’s about real lived family life and how the tiniest details are made of magic.

A secret world of a very different kind is explored in Bernadett Tuza-Ritter’s A Woman Captured, in which she gains unprecedented access to a middle-aged woman being kept as a domestic slave in Hungary. This film will make you cry.

Elsewhere, and also likely to provoke tears, Bing Liu’s debut feature Minding the Gap offers tender stories of a group of Rust Belt skateboarding boys as they become men and have to deal with the troubles that a board and your friends can’t solve. There haven’t been many better documentaries about sensitive masculinity; there’s a beautiful lack of sentimentality to Bing’s depiction of time passing too quickly for comfort. There’s a similar sense of the perils of nostalgia in Shirkers, Sandi Tan’s joyous love letter to the tiny independent film scene in Singapore in the 1980s. It simultaneously revels in and mocks the naivety of youth and teenage friendships. Look out for the dancing dog.

Doc/Fest always features a particularly good selection of films skirting the borders of art and essay. I’m excited by the return of philosopher-artist Astra Taylor. Her What Is Democracy? will feature musings that will hopefully make us feel a bit less desperate about being citizens. Taylor’s documentaries, like her books and journalism, are always impeccably researched and even funny and entertaining where they could so easily be dull, one-dimensional activism.

Outside the main festival competitions are two near-uncategorisable films coming from what feels like outer space. Josh Appignanesi’s Female Human Animal features curator Chloe Aridjis’s entirely real exhibition about the surrealist artitist Leonora Carrington, but sets it against a fictional story of psychosexual obsession, devised with and starring Aridjis. To further confuse viewers, it’s shot on an old video camera. It’s trying something truly bizarre that punctures the pretentiousness of the art world while also, of course, being rather pretentious – and it’s a triumph.

This successful, if odd, experiment feels like a distant cousin of Peter Watkins’s La Commune (Paris 1871), revived by Doc/Fest 18 years after its initial release. Watkins restages the revolutionary events as if they were being filmed for an observational documentary, and it’s entirely convincing. It’s nearly four hours long but worth every minute.