It tries to look at food production as a global system, the successes it's had in terms of making food more affordable and avoiding global famine, but also the damage it's causing to climate and biodiversity, and possible ways forward given the constraints of making food production sustainable without creating mass starvation.
I will also say that many groups of people don't like the conclusions. Many farmers and meat eaters don't like the idea that livestock farming at the scale needed to support modern western diets is fundamentally unsustainable. People who believe that eating free range meat means that they've made the clearly ethical choice may be surprised at how that works out over an entire population. Many non meat eaters are uncomfortable at the argument that just hoping people switch to vegan diets is unlikely to work in practice. Many environmentalists don't like the conclusion that the best hopes for a way forward involve more technology, not less.
I'm not sure he ends up betting on the right horses, but it seems to me that the substance of the book is well thought through, and hard to disagree with without falling into the "let them eat cake" trap that's called out in this essay.
[1] https://www.penguin.co.uk/books/317018/regenesis-by-monbiot-...