There's so much Steven Soderbergh wanted to say about Che Guevara that he needed two films to say it. Yet he claims the personal life of the iconic revolutionary who helped Fidel Castro overthrow the tyrannical US-backed Batista regime in Cuba in 1959 doesn't mean all that much to him. "I guess I never really looked on it as a biopic," he says. "At the end of the day, I was less interested in him and more in what he did. I was more drawn to the procedure of the revolution than I was necessarily to Che's ideology. What intrigued me was how did they do this?"

Che, which is in Spanish and was filmed with non-American finance in Puerto Rico – involving several visits to Cuba that required State Department approval – is a classic rise and fall narrative showing Guevara's charismatic brilliance in orchestrating the triumph of Castro, and then his desperate folly in trying to impose a similar revolution on oppressed peasants in Bolivia. It divided critics at Cannes, where it screened in a single 268-minute late-night session, but will release as two films in Ireland – Che: Part 1 opens on 2 January, and Che: Part 2 on 9 January. While it didn't start out as two films, it's probably how it works best: either way it's a riveting study of how revolutions succeed and fail, and provides clues to why Castro's Cuba has not only survived but may yet achieve a peaceful transition under his brother Raul – a crucial figure in bringing him to power.

Benicio del Toro originally approached Soderbergh with the idea of portraying Guevara's last days while they were filming Traffic. "We knew Terrence Malick had been in Bolivia when Che was killed, and was trying to write a story about him. It was obvious he was interested not only in writing a script but in directing it too, so I stepped aside. Then Terry had to finish The New World. All the deals that were set up would fall apart if Che didn't have a director right away. So I came back on."

At that stage the idea was just to show Bolivia in 1967. "But I felt if you didn't see the revolution in Cuba, you wouldn't understand Bolivia. I wanted to see Che go from the asthmatic doctor to the T-shirt. But it then got too big for one movie so I took a cue from nature, which is when a cell gets too big it divides. I just chopped the thing in half."

Guevara saw revolution as a kind of brand that could be exported, much as the US franchised its brand of democratic capitalism. "It's obvious to us now, but it's surprising it wasn't more obvious to him - that without an indigenous leader you can't pull this off. You can't just show up and tell people what they want. Fidel was already famous when he came back to Cuba. People were waiting for him. For Che not to comprehend the importance of that is startling and to my mind played to his hubris. I really think he thought that at a certain strategic point when he revealed his identity to the Bolivian peasants, everything would turn around."

Che 1&2 might seem a surprising change of direction for 45-year-old Soderbergh, creator of the enormously successful Oceans franchise and winner of a best director Oscar for Traffic in 2000 – he was also nominated that year for Erin Brockovich, the first double nomination in 60 years. But the only predictable thing about him is that he always surprises.

Back in 1989 when he became, at 26, the youngest winner of a Cannes Palme d'Or with his $2m debut, sex, lies and videotape, he famously predicted it would "be all downhill after this." As it happened, his career has been more a matter of valleys. "You can't just leap from mountain top to mountain top," he says. "In my experience when you're talking about an art form, there are no short cuts. You have to put the time in. I luckily grew up in a period where you could still make failures and not have people punish you. Young film-makers coming up today don't get as many chances as I got."

He's learned more from failure than success (see panel). "Success is like meeting some woman in a bar and you don't know where she came from, you just love her conversation and it's all going great and everything you say is funny. You go home with her and you wake up and she's gone and you don't know who she was or where she came from. But failure is like the guest who will not leave. I decided to take advantage of that and analyse it – failure was hanging around so often, not in terms of what the audience wants to see, because that's always a question mark, but in terms of the thing itself."

Through constant experimentation he's developed a cinematic language and way of marrying form to content that feeds back into mainstream films like Out of Sight, the first of six films with George Clooney, making him one of the most bankable directors in Hollywood while still remaining true to his independent origins. "I'm not an original like Altman or Bergman or David Lynch, I'm just not. I'm a synthesiser. I can soak up a lot of stuff and I can organise it and come up with a way of unifying it that makes it seem organic. That's what I'm good at."

It's not how he imagined himself back as a precocious teenager directing Super 8 films with equipment borrowed from students at Louisiana State University, where his Swedish father was Dean of Education. "I think everyone has a fantasy when they begin that they are one of those original people who move the bar forward or upward. At a point in my career when things were not going well and I wasn't happy with what I was doing, I had to sit down and figure out why that was. I realised people were born to be original and I wasn't born to be that."

Next spring he hopes to film Cleopatra, a musical with Catherine Zeta-Jones in the title role. "I knew on Traffic, even before she did Chicago, that she was a song-and-dance girl. I've been thinking about doing a musical my whole career." He's just completed The Informant, with Matt Damon as a real-life corporate whistleblower – "it's a comedy, by the way, I don't think a lot of people know that" – and is in the middle of shooting The Girlfriend Experience in Manhattan with adult film star Sasha Grey.

"She's going to amaze people," he says. "It's a $2m production with a crew of 12 and one truck with our gear in it. It connects me right back to the first thing I ever did, and the energy and enthusiasm of the amateur. I still like the Oceans films, but there's something great about just being a small band of people with a camera.

"I've still got a couple of things coming that I'm excited about – maybe a sports film – but then at a certain point, sooner than people would imagine, I'll just stop, because I'll feel that I'm repeating myself. It'll be time to do something else. I'll be done."