G. is in my opinion the best novel ever to win the Booker Prize. What's not in dispute is that it's the only Booker-winning novel whose author announced in his acceptance speech that he intended to give a large chunk of the prize money to the Black Panthers.
I have always been baffled by people who claim that G. is "incomprehensible", "pretentious", "turgid", or whatever. Compared to most novels, G. is a masterpiece of clarity. Most serious novelists have swallowed more ideas than they can stomach and have failed to digest them, hence the clotted and unreadable quality of your average Booker-nominated doorstop. Berger knew exactly what he was doing with G., and only the fact that it's laid out in discrete paragraphs makes it look more "experimental" than it truly is. This was the early 70s, when people like B.S. Johnson and Christine Brooke-Rose were all the rage in Brit fiction, writing self-consciously difficult novels according to their own rather weird theories about the nature of writing. It was B.S. Johnson who famously remarked that the lesson he had learned from Joyce was that it didn't matter what you wrote about - the only thing that mattered was how you wrote. (Johnson also somewhat contradicted this dictum by insisting for years that all good writing, his own in particular, was obliged to be more or less autobiographical, on the grounds that making stories up is in some way dishonest.)
Berger was not at all interested in such sophistry. He wrote G. the way he did because he was compelled to. He was and indeed still is a distinguished left-wing art critic who had also written one great first novel and two startlingly bad successors. In G., he wanted to combine historical analysis and realistic fiction, because the material he was writing about demanded it. He wasn't the first person to do that. Tolstoy lards great wodges of didactic historical commentary into "War and Peace", which is also a gripping family drama and an exciting war story. All throughout G., Berger skilfully weaves quotes from other writers in such a way that you seldom notice (and don't need to know) that they're not integral parts of the book. (This itself was not unprecedented; Georges Perec's second novel Un homme qui dort was a patchwork of modified quotations from other writers.)
G. is Berger's last attempt to write fiction about the kind of people who were likely to read him. The early 20th century setting should not blind the reader to the fact that we are much more like the characters in G. than we are like the peasant and working-class characters of his later Into Their Labours trilogy. G. is an entirely successful attempt to hold a mirror up to the reader, and as Oscar Wilde predicted, most readers prefer not to be shown themselves - hence the panic and rage some people feel when they read the book. As a mordant, historically aware, unsentimental and yet compassionate account of the moral and political blindness of middle-class society in a certain time and place, this book has never been bettered. Formally, it's one of the most elegant books Berger has written. The prose is among Berger's most imaginative and daring writing. The sex scenes are the more effective for not being erotic. They don't turn you on, because they aren't meant to: they tell you what the sex meant to the people involved. The hero of the book is one of the strangest characters in modern fiction, powerfully present and yet curiously blank. The book haunts you. No other novel I know of, by a living English writer, has such an effortless command of both grand movements in history and intimate domestic detail.
Berger's next book was non-fiction, about the plight of migrant workers. He didn't return to fiction until the late 1970s, since when his novels and stories have focused on the poor, excluded, marginalised and oppressed. I think that some of his later works, (Pig Earth, Lilac and Flag, To The Wedding, From A to X) are as good as, if not better than, the novel that won him the most famous literary award in the English-speaking world nearly four decades ago.
(Why did Berger give Booker money to the Black Panthers? Because Booker-McConnell, who were the prize's sponsor back then, used to have massive investments in sugar plantations, and a dodgy history when it came to worker exploitation in the sugar industry. That was a few takeovers ago. They have since cleaned up their act a bit, and are now a major wholesaler to the catering and retail industries.)