Strauss and Howe have written several books since this one, expanding upon their general historical thesis. But this one is the seminal book, the important one, and the one on which the others are based.
The book basically is a theory of American history that is premised on generational behavior. The authors have been quite successful in explaining and in some instances predicting the cycles of events, values and opinions of American society. It's very much worth reading simply because the reader is likely to experience an enhanced understanding of what is happening around him/her in the body politic.
The basic insight in this book is a simple one: Instead of trying to build a theory of American history (as did Arthur Schlesinger) that is based on unexplained "cycles" and "swings" from liberal to conservative and back again, why not simply look at how American generations behave as they age? When you do that, as Strauss and Howe have found, you find that American generations behave with a certain consistency throughout their lives. If their formative experiences push them in a certain direction while young, they'll continue to act in that way as they get older. That is, if you understand that history is really the process of different generations moving through time, then the swings of American history no longer look so mysterious; they appear as predictable manifestations of the fact that different generations with different life experiences have risen to the foreground.
Of course, you don't want to take all of this too sweepingly, or else it starts to seem like astrology or historical biorhythms. Generations are diverse groups, and no two people within a generation are exactly alike. But there are clear trends of generational behavior, which Strauss/Howe substantiate quite well.
Their basic model is that there are four basic generational types, which tend to occur in this order: Idealist, reactive, civic, and adaptive.
The GI generation (born 1902-1924) that fought WWII is a classic example of a "civic" generation. Consider their life experiences; when they came of age, they were asked en masse to participate in the greatest government-directed effort imaginable, fighting and winning WWII. Then when they got done with that, many of them went to school on the GI bill. When they were young, government spending and focus was oriented on youth. When they aged, government spending and focus shifted along with them, to where it is now focused on their elderly group, through Social Security, Medicare, and the other elderly programs that dominate the federal budget. It was natural that this generation would come to think of government's priorities being oriented in their direction as the natural order of things. They are civic-minded and they tend to have a more benign attitude towards government than do other generations. Accordingly, they are generally suspicious of change in the government approaches they know (for example, strongly against Social Security personal accounts, as opposed to a government-defined benefit.) Also, as a civic generation, they didn't focus their energies on redefining the values and purpose of America, they had a job to do (win the big war), and they did it.
Contrast that with an "idealist" generation, the "boomer" generation. Many in this generation grew up with an assumption of unlimited economic opportunity and security. They therefore turned their attention to spiritual matters, questioning and often rebelling against the values of the GI generation as well as its follow-up generation, the Silent generation. It was this "idealist" element of the boomers that unleashed the social revolutions of the late 1960s. This streak of strong opinions is visible in the boomers to this day; many of the political leaders who are regarded on both sides as being among the most shrill and uncompromising are from the boomer generation. This was also true when they were youth in the late 1960s; not only the activists on the radical left, but also those who retreated into a dyed-in-the-wool conservatism. The Silent generation prior to them didn't generally split into such poles.
The contrast between the "Silent" generation and the boomers is instructive. The "Silents" followed on the GI generation, looked up to them, generally shared their values, and sought to expand and liberalize them somewhat incrementally. The "silents" worked within the system: the 1950s, for example, saw civil rights expanding, Brown vs the Board of Education, etc. They sought to expand the blessings of liberty but at the same time were generally trustful of the leadership of previous generations. Not so the boomers; as the boomers came of age, they loudly, and often with great hostility, attacked the core value systems of the generations before them as being inadequate to progress, and sought to make a new, purer system of values. The silents wouldn't have been nearly so bold.
You can see the results in our national politics. The GI generation dominated the presidency for some time (Kennedy, Nixon, Carter, Reagan, Bush the Elder) and then handed the baton off to the Boomers (Clinton, Bush the Younger.) The Silent generation was simply skipped over.
The so-called "Generation X" (1961-81 birth years in this book) is a classic example of a "reactive" generation. These generations usually followed idealist generations, and didn't have the economic optimism of their predecessors, and thus didn't feel the same security to reimagine the spiritual basis of their nation. These generations often receive great criticism from the generation before them for failing to uphold their ideals. When the Strauss/Howe book came out, this was happening to Gen X much more than is the case now; the boomers, anxious to preserve their spiritual vision, often expressed concern and even disgust about the cynical, world-weary attitudes of the generation that followed them. But the Gen xers had had a different experience; they were not taught, as were the boomers, that life was always going to be sunny for them economicallly. The boomers were blocking the job pipeline as these Gen Xers entered the workforce for the first time. And their life experience with government is exactly the opposite of the GI generation;at every stage of the Gen Xers maturation, government's resources have been directed to benefit someone else. Whereas the GIs will get far more out of Social Security than they ever put in, Gen X will put far more in than they will ever get out; small wonder that Gen X generally wants to be given personal accounts instead of sticking with the old system.
Only over time have the Gen Xers won the respect of previous generations, just as did previous "reactive" generations of their type. A great analogy are the generations that came of age before the American Civil War. The analogues to the boomers then were the "transcendental" generation: the Thoreaus and the Lincolns and the Garrisons -- many of the abolitionists and civil disobedients who found the value system of their nation to be lacking. They unleashed a social revolution that exploded in the Civil War. Meanwhile, the generation behind them, the Ulysses Grants of the world, were thought to be mundane, unimaginative, unimpressive. But it was the Grant generation that fought and won the Civil War, relying on the resourcefulness that a tougher life had required them to learn. The Gen Xers are showing similar resilience now.
As said, you can't take any of this too exactly; otherwise it starts to seem like the Chinese zodiac; it's not the case that everyone born in the Year of the Bunny is lucky and affectionate. But it is still the case that formative experiences are often a key to understanding generational behavior. Strauss and Howe provide a very useful way to think about history, and an entertaining book to boot.