As Plato said, "The unexamined life is not worth living," so the key theme here is that we must constantly be looking beneath the surface of our lives. It's heavy stuff, but the film is assembled with a light touch as it follows philosophers around major cities. West's clips are scattered through the film, talking from the back seat of a car in New York about how our human finiteness is the defining element in our quest for truth, which means we need to cling to each other even in the most difficult situations.

We also have the witty Ronell walking in a park talking about how life's journey is more important than any meaning we apply to it; Appiah strides through an airport talking about how our lives affect the whole world; Nussbaum strolls along the Chicago lakeshore discussing social and natural divisions between people; Hardt rows a boat in Central Park thinking about the human desire for revolution; and Butler and Taylor walk through San Francisco chatting about how judgmentalism and ignorance leads to isolation that disables all of society.

Most memorable is Singer, strolling down Fifth Avenue questioning how we spend our money from a remarkably honest angle: we're annoyed that we ruin our good shoes rescuing a drowning child, yet the money we spent buying those shoes could have saved the lives of 100 children in poor countries. And then there's the colourful Zizek on a London rubbish heap noting that we are all part of nature yet somehow believe our trash magically disappears because a bin-man carries it away.

The most remarkable thing about this film is the way it's never weighed down by its own importance. Everything is presented conversationally, so even if we miss the academic references we're challenged by the ideas. It's also beautifully well-made, with lush photography and a pulsing score that punches some mind-stretching messages, such as questioning whether ethics are worth anything if someone tells you what's right or wrong (Ronell) or asking whether we really care about people who are different from us if we love them on our own terms (Appiah). Yes, it's a film that can haunt you for the rest of your life.

There's a remarkable amount of information here, and filmmaker Kenner assembles with clarity, building our outrage as he goes. We see how the way we eat has changed more in the last 50 years than in all of human history before that, and yet we delude ourselves with the "pastoral fantasy" that what we consume still comes from farms. The reality is that food is a mega-industry: they're factories, not farms, and it's a product, not a living chicken.

It's pretty shocking to see how we're fed an illusion of diversity even though almost everything comes from a handful of corporations that are cleverly rearranging corn products. Of course, the industry doesn't want us to know this, so they've become expert myth-spinners, creating laws that keep us from finding out about hideously huge farms, enormous assembly lines and the real reasons for outbreaks of E coli and salmonella (blame giant farms and assembly lines). This is a skewed system in which a double cheeseburger is cheaper than a head of broccoli.

Specific stories about Tyson (the world's biggest meat supplier) and Monsanto (which has ruthlessly patented nature for profit) are utterly chilling. And the film also addresses labelling, how increased sugar content undermines public health and the effect of big industry on trade, working conditions and immigration. In short: someone has to pay the price for our cheap food.

Kenner also assembles a terrific collection of people on camera, including Fast Food Nation author Schlosser, rebel farmer Salatin and food safety advocate Kowalcyk. Besides presenting facts, each takes a personal approach, reminding us that this is something that affects us every day. And Kenner includes some witty animation, gorgeous scenery and deeply unsettling footage to keep us glued to the screen.

This is a seriously important film, exploring many of the same issues as Michael Moore's Capitalism: A Love Story. The main question is whether well-fed people would rather have cheap food than a fair society. And if Americans feel powerless to get their government to take action after decades of letting the industry avoid responsibility, they need to remember that this level of control can be broken: just ask Big Tobacco.

In December 2007, Ben Freeth comments about his father-in-law Mike Campbell that "it's quite surreal that someone as gentle as Mike will stand up to someone who has brought death to thousands". And yes, Zimbabwean president Robert Mugabe wants Campbell and his family out of the country, but they have called their farm home since 1974 and refuse to leave without proper legal authority. And they're willing to take this to a regional African court to establish a precedent for the entire continent.

Mike and Angela and their daughter Laura and Ben note that 500 farm workers will lose their livelihood if the government seizes their land, and they stand firm even when government thugs come to beat them up. And this is exactly what happens following Mugabe's 1997 edict, with chanting mobs, threatening fires and burly goons threatening (and delivering) physical violence. Step by step, the reaction of the Mugabe government is mind-bogglingly nasty; you simply couldn't make this up.

Filmmakers Bailey and Thompson tell the story as a riveting thriller, complete with action, suspense and legal intensity. And as Mike and Ben set out to probe that Mugabe's "land reform law" is unfairly racist, they face a shocking display of political oppression. The truth is that no black farmers have lost their land and no white-owned land has actually gone to farmers. It's all gone to government relatives and cronies.

As horrific as it is to watch innocent people tortured and stripped of land they worked all their lives to own, there is still an underlying hopefulness that peace will come to their land. This hasn't happened yet, and the film traces the remarkable story with first-rate photography, expert editing and an astute sense of storytelling. Much of the film was shot covertly to avoid imprisonment, and yet the quality of the images never suffers as a result: this is as urgent and exciting as movies get.

And beyond entertainment value, it's examining both an intensely important news story and potent themes that apply to all of us. And the Cambell's astounding bravery can't help but inspire us. Stretched by their faith, they believe they have a purpose in this fight against injustice, and the film vividly catches the emotional and momentous tone of what happens as a result. It's a seriously involving story, and an unforgettable film.

Followers of the English band Depeche Mode clearly believe that the music speaks specifically to them. From Mexico to Russia, these fans imagine the band's hometown Basildon as an artistic paradise, blithely unaware of its grim urban reality. Not to mention the fact that most people who live there haven't a clue that Depeche Mode grew up there. But over the past 20 years, the band has inspired passion everywhere its music is heard.

The filmmakers gather a remarkably wide range of fans here, from the T-shirt collector in New York (Easton) to a young Iranian (Peyman) who listens to illegal tapes. There's the vicar (Watts) in Cambridge who uses the music in services, the German family (the Granzows) that re-enacts their videos, a Moscovite (Bobileva) who draws cartoons of her life, the formerly homeless Londoner (Constantine) who claims the music saved his life. We also meet fans in California, Bucharest and even Basildon.

And the film is packed with wonderful moments, as fans in St Petersburg celebrate band founder Dave Gahan's birthday, which conveniently falls on the same day as their big military parade. Watching them marching down the streets singing Enjoy the Silence is pretty amazing. The title refers to the Berlin police who tore the band's posters from the walls before anyone could see them when they played the first Western gig in Communist Germany.

The film is extremely well-directed by Turner Prize-winner Deller, with witty photography and editing. It's packed with lively scenes of wallpapered bedrooms, street parties and fans with huge personalities. There's also great footage of the band performing, as well as of the fans singing the songs in their own style (including reading lyrics out in the style of a darkly Russian poem). And the filmmakers find terrific political subtext in several sequences, both putting the band's history in context and showing why their music has meant so much to two generations of fans. And counting.