The story goes that French-born Thierry Guetta, a Los Angeles shop owner, is videotaping everything he sees and becomes obsessed with street artists like Space Invader in France and Shepard Fairey in America. Doggedly documenting their illicit work, Thierry sets his sights on the leading light of the movement, Britain's Banksy, and eventually they team up to take L.A. by storm. Then Thierry abandons his filming to become an artist himself, marketing his work until some 7,000 fans turn up for his first Hollywood show. Which leaves Banksy to finish the documentary.

Watching this film, we can't escape the growing feeling that this is all a con. Not only is Thierry just a little too nutty for words, but his rise to fame bears all the hallmarks of a lacerating satire of the art world's obsession with anything new, even if it only steals from everyone else. Thierry's artwork, which is created by a team of PhotoShop experts on his instructions, is a mash-up of street artists from Andy Warhol onwards. He goes by the name Mr Brainwash, saying that his art reflects how iconic images affect us. Or is he the one brainwashing us?

Whether this film is fiction or documentary is frankly irrelevant, as it establishes Banksy as a gifted filmmaker with a cheeky sense of humour that matches his clever work both in the streets and in art galleries around the world. It's an expertly shot and edited movie, with camerawork that seems perhaps a bit too expert for the wobbly Thierry.

It's also packed with vivid characters and a sharp sense of anarchic humour. Banksy and some other street artists make sure their identities are disguised by shadows, pixels or camera angles, because it's their art that matters and their refusal to stay within the law is part of what makes their work so iconic. In other words, this is one of the most important movies about art ever made. And it's also one of the most enjoyable.

When Gruff Rhys, frontman for the Super Furry Animals, realises that noted Welsh-Argentine singer Rene Griffiths is a distant uncle, he decides to find out more about his musical heritage. He traces it back to an 1880s scandal that split his family and sent one branch to join a Welsh community in South America. So Rhys heads off to Brazil, Buenos Aires, Patagonia and the Argentine Andes, meeting Welsh descendants along the way, many of whom still speak the old language. And virtually all of them are musical.

As he travels, Rhys plays a series of offbeat gigs for the people he meets, mainly witty electronica and folk tunes, all in search of his own musical legacy. We also see the locals' performances, plus footage of Griffiths' 1970s tour of the UK, which was documented by the BBC. There's also a brief history of the interaction between these Welsh expats and the indigenous people. And all of this is intriguingly linked by music and culture.

Rhys hosts the film as if he's travelling through time and space with the help of a bright red Power Rangers-style helmet. As he pops in and out of various locations, we get a sense of connection between these two different lands. The new footage of Rhys' journey has a scruffy charm that captures the raw physical beauty of the various landscapes, often prismed into drifting split-screens. And there are plenty of stills and archive clips to give us glimpses into the past, as well as a few lively re-enactments.

The film has a smart and inventive style, and a lot of warmth and affection, but it also feels rather freeform and aimless. Sure, there's this central quest to find Griffiths (which leads to a couple of terrific gags), but watching it will require patience with Rhys' distinctive sense of humour. And it also helps if you have an interest both in Wales and in South America's complex colonial history.

Unsurprisingly, Stone's main target is Fox News, which gives its usual shameless slant to stories about Latin America, referring to democratically elected presidents as "dictators" and blatantly painting them as Communist criminals. According to polls, some 70% of Americans believe these lies, which blur leaders like Chavez with the likes of Osama Bin Laden. Stone blames much of this on American arrogance in the wake of the Soviet Union's demise, and he also makes the connection with global capitalism, as US "interests" push nations to surrender their sovereignty to the International Monetary Fund.

But of course the story is much more complex, and Stone narrates the history through early clashes between Chavez and the US-supported hardline Venezuelan government, a scene that echoes later with Morales in Bolivia, Da Silva in Brazil, Correa in Ecuador, Lugo in Paraguay and the Kirchners in Argentina. In other words, the US has worked to undermine democracy simply because it means they lose control of the country in question.

This is a vitally important issue that needs to be brought to light, as it vividly shows the rampant hypocrisy in the US government and how American media are manipulating a gullible public. Stone documents everything carefully, showing the brutal history of CIA assassinations over the decades and how this backhanded imperialism has kept South America under the north's thumb. So as these nations band together as Bolivarians, harking back to a previous battle against a colonial power, it's no wonder that US big-business is waging a propaganda war while the American government engages in politics of control.

With such strong material, it's a shame Stone doesn't quite tell the whole story. His approach is extremely one-sided, never entertaining criticisms and refusing to ask tough questions of these lively and charismatic Latino (and one Latina) leaders who had the nerve to stand up to George W Bush and the IMF. These are smart and clever people who are demanding equality and respect: two things they are due regardless of Stone's political leanings.

In 1924 George Mallory and his climbing partner Andrew Irvine died while attempting to climb Mt Everest, something no one would do for another 30 years. The mystery about whether they reached the summit actually deepened 75 years later, when climber Conrad Anker discovered Mallory's body on the mountainside, complete with a clue hinting that he and Irvine were on his way down from the top. So Anker finds his own inexperienced sidekick in young Brit Leo Houlding and sets out to retrace their steps to see if they could have made it up the notorious Second Step.

Within this narrative, Anker and Houlding also recreate the conditions by wearing period-style clothing. This is then crosscut with actual footage and stills from the original expedition, while on the soundtrack we hear the text of letters written back and forth between Mallory and his wife (voiced by Fiennes and Richardson), Irvine (Dancy) and their friend Noel Odell (Rickman).

All of this pieces together the remarkable story of these intrepid men and the conflict they had between their families and their love of climbing. And this is also echoed in the modern-day footage of Anker and his wife (who lost her first husband in a climbing accident) and Houlding and his girlfriend. It's a simple but beautifully assembled film, full of reflective moments and visually powerful moments.

And it also catches the spirit of Mallory, the man who first said, "Because it's there," in reply to a journalist asking why he was climbing Everest. The filmmakers piece together details of the parallel expeditions 83 years apart, following the same route step-by-step. It's thoroughly captivating, and yet it also feels like something we'd see on the National Geographic Channel on a Saturday afternoon. Perhaps if the new footage had been shot in Imax ratio it might be more cinematic. Even so, it's a terrific examination of obsession and dedication, the importance of family and the enduring legacy of a true pioneer.