I had heard that this film was long and boring, but I eventually saw it out in the Lighthouse. It is long, but I found it anything but boring. It follows Guevara's war against the Batista dictatorship, intercutting this with a visit Guevara made some years later to address the UN as a representative of the Cuban state. The film does cast Che in a rather heroic light, seeing his guerrilla war as like a succession of relatively easy victories against the shifty servants of dictatorship. At the same time, it does not present him as winning the war single-handedly – as well as getting a sense of there being other important commanders in the fighting (e.g. Fidel Castro himself, Raul Castro, some other guy with a beard, etc.), you also get a sense of how dependent the war effort was on the movement's rank and file. The rebels' base is portrayed as having its own inspirational figures, people motivated by a desperate urge to transform their lives and social situations.
I am looking forward to seeing Che, Part 2. That covers his Bolivian campaign – his failed attempt to export revolution from Cuba to the heart of the South America continent. The first film shows a guerrilla army that keeps winning, while the second apparently shows Guevara's band failing to make headway and then finding the enemy's screw tightening. So we see Che's triumph in part one and then his downfall, missing out any of the less appealing aspects of his life – his virtually Stalinist outlook, his embarrassing adventure in the Congo, his presiding over politically driven executions of Cubans associated with the former regime, and so on. But hey, I know about all that already – I do not go to the cinema for a history lesson.
I suspect that you could enjoy each of the Che films independently of each other, but I would recommend Part One to people who like cinema.