This is a useful book for scholars but the chapters are a bit of a mixed bag. The overall themes that come out of the book, however, are very useful for thinking about what the radical right is as well as the tensions with in it. It starts with sort of classic far right thinkers like Schmitt and Spengler and goes all the way up to the present day (well, 2019) to weirdos like Mencius Moldbug and Richard Spencer.
A few of the major themes from these thinkers: They are all fundamentally illiberal, in that they do not believe that human beings are created equally and are deserving of the same rights and opportunities. They believe at a normative level in hierarchy, domination, and different forms of cultural/racial purity. They are mostly quite uncomfortable with modernity and the administrative state, which they believe homogenizes society and crushes individual spirits (they also believe it has been hijacked in most cases by liberals). They are almost exclusively anti-democratic, viewing democracy in a NIetzschean way as a sort of herd morality. They often have a romantic streak, believe that life is about struggle and heroism but that the modern world suffocates these things. They are mostly traditionalists and nationalists of some kind, although a few are futurist libertarian types associated with Silicon Valley radicals like Peter Thiel. Some of them are out and out biological racists, while others are more of the belief that different races or cultures are not meant to mix and that multiculturalism leads to national or racial degeneration. Either way, this mentality leads to some form of white nationalist, nativist, even eugenic politics. They are also cultural particularists who believe that human values and lifestyles should not be applied to other societies, even if some of them don't vehemently believe that the West is necessarily better than other cultures.
A few other themes: they are deeply concerned with decline, decadence, and even national or racial suicide; this is the Spenglerian tendency among them, although Spengler didn't endorse outright racist. THey have mixed views about CHristianity, although they tend toward the negative belief that Christianity is the root of liberalism's endorsement of universal human equality or a form of slave morality. They are also quite mixed on capitalism: some see it as a liberal, cosmopolitan system that erodes national boundaries and unique cultures, while others are more libertarian and want to unleash. They are, as you might expect, almost all men who are deeply concerned with masculinity in the modern world.
The final big theme for them is metapolitics, which is their main political strategy. This term arose in the postwar French far right, and it is their long-term strategy for unseating liberalism as the dominant mode of politics and thought in the world. They argue that liberalism is so dominant now that direct participation in politics as the far right or white nationalist parties is premature; they are just doomed to lose and might actually feed liberalism's energy (there are of course far right parties across the West that in some cases draw on aspects of the radical right's). SO instead, they argue for building up radical right ideas in the culture, media, internet, etc so that over time liberalism's legitimacy becomes eroded and you can actually build a political movement. This is a Gramscian approach to politics that has become ever more influential on the right. But it isn't clear how much it is working, and it might just be an excuse for these weirdos to mostly stay within their existing circles and avoid the public spotlight (many of them are terminally online nerds).
This book was helpful for showing just how much the RR differs from mainstream conservatism, even as they have become more blurred in the last decade. However, I wouldn't recommend it to non-specialists. Some of the chapters aren't very good and/or just weren't translated well. There's a lot of thematic overlap between chapters, as most of these dudes aren't all that different. For more holistic and thesis driven studies of the Radical Right, see George Hawley's "Making Sense of the Alt-Right" or Matt Rose's "A World After Liberalism.