Way back at the beginning of Heinlein's writing career his editor at Astounding, John W. Campbell, published the 'Future History', a two page listing of Heinlein's projection of the significant individuals and scientific, economic, and political events of the next 700+ years, along with a list of story titles that brought each of these events to life. At that time, most of those stories hadn't been written, and from some of the notes and statements in interviews that Heinlein made in the fifties and sixties, it looked like some of those originally projected stories would never be written, most significantly the final entry, "Da Capo". Finally, in 1973, when everyone had given up hope, this book appeared, a book that put the finishing touches on the Future History, a book that closes with that final story.
But before reaching that final story, we are given a cornucopia of other stories, as Lazarus Long, now some 2300 years old, is induced to reminisce about his life as part of a complex deal to preserve the 'wisdom' of the oldest man alive. Each of the stories that Lazarus relates are fairly complete by themselves, and many authors would have chosen to publish each of them separately, but Heinlein chose to keep them all as one piece, as each story helps to illuminate his overriding theme, on just what is love in all of its myriad aspects and why it is so important to man's survival as a species.
The first of the tales, "The Man Who Was Too Lazy to Fail", may be the weakest of any of the stories, but for those who know something about Heinlein's life, this story is very clearly autobiographical in nature, with some changes in names and places to protect the innocent.
"The Tale of the Twins Who Weren't" brings to light the ease with which Heinlein could switch between first and third person along with some detailed commentary on genetics and the reasons incest is normally consider taboo, all neatly folded into a story of individual growth from illiterate slave to successful entrepreneur.
But the next tale, "The Tale of the Adopted Daughter", is worth the price of this book all by itself. A very quiet, simple tale of pioneering that would not be out of place sitting on the Westerns shelf, though it has a unique science fictional aspect - but by the end of the story tears are definitely in order. The excellence of this story can be judged by the fact that its emotional impact is not lessened even on second, third, and fourth readings, when you know exactly how it ends. This story does much to illustrate that love is far more than just sex, although there is certainly a lively interest in that oldest sport displayed by all participants here.
The outer story in which these stories are embedded like sparkling diamonds evolves from a pretty standard plot device for presenting back stories to an intriguing story of its own, as we follow the attempts of various and sundry to give Lazarus a reason for living again, to find some new experiences that are not just a rehash of things he has done a thousand times before.
But it is also this 'present' time story that leads to the objections that many people have with this book: its apparent near-obsession with sex between close relatives. In one case it is more than close, it is narcissistic, dealing with Lazarus' relations with twin female clones of himself. It seems that many see only the sex, and don't look beyond it to the larger picture that Heinlein is presenting of all forms of love, including some essentially platonic forms, and that all of them can provide a means for 'growing closer' with another and enriching the lives of all involved.
In-between these stories are the 'Notebooks', a collection of aphorisms and other 'pearls of wisdom' that Lazarus has supposedly collected during his long life. Many are humorous; just about all of them have a spike of truth curling through them. My favorite of this group is probably "A committee is a life form with six or more legs and no brain" or possibly "An elephant: a mouse built to government specifications" but everyone will probably find something here that is appealing.
The Notebooks are some succinct examples of something that Heinlein scatters throughout this book, his opinions on government, slavery, marriage, politics, revolutions, prisons, family organizations, the value of money, 'consciousness' both organic and computer based, betting, Darwinian selection, true 'intelligence', conscription, advertising, religion, the purpose of war, and just about every other subject you can imagine. While you may not agree with many of these opinions, Heinlein presents his views in such a way that you will be forced to at least examine why you believe your own opinions are correct.
And finally we come to the last section of the book, where Lazarus time-travels back to meet his parents in the Kansas City of 1916. Heinlein manages to create a beautiful image of that time and place, its moral codes, its hypocrisies, its charms, of an entire way of life that has just about totally vanished from the American scene. Few fictional histories approach this section for being able to put the reader into their chosen time frame.
This book is the capstone to the Future History, apparently planned at least in part when the History was first conceived, a remarkable achievement in scope, theme, and sheer story telling. It was nominated for the 1974 Hugo Award, and fully deserved that honor.
Edited July 2014: While reading William H. Patterson's Robert A. Heinlein: In Dialogue with His Century, Volume 2: The Man Who Learned Better, (highly recommended reading for any Heinlein fan, along with the first volume of the biography, Learning Curve ), I came across the statement that "The Man Who Was Too Lazy to Fail" episode was not based directly on Heinlein's own experiences but rather on those of an Annapolis classmate, Delos Wait. As Patterson has been extremely meticulous in his research on Heinlein's writings, I will go with his version for the source of this story. Regardless, the story does have points of intersection with Heinlein's own experiences, some of which ended up of the pages of many of his other books.