It's not Robert Heinlein's fault this book was published. He tried to destroy every remaining copy of the manuscript before he died. It was his first attempt at a novel, and lacks one of its most basic requirements, a plot. (The same could be said of some of his late novels, without the excuse of inexperience, but that's a different department.) Its audience is Heinlein completists and readers who want to discover some of the seeds of his later work.
The book was apparently written in 1938, the year before his first published story, "Life-Line," was accepted. (This was just two years after the appearance of Ayn Rand's We the Living, but that's probably just coincidence; Rand's book was not hugely successful when first published.)
The premise is that an engineer named Perry Nelson has an accident in 1939, then awakes in 2086 in another man's body. What follows isn't a story so much as a series of lectures on life in that future world. It's a very imaginative world, to be sure, and the description of the events leading to it -- in effect, a first draft of Heinlein's "future history" -- provide some of the most interesting pages. But it's a chimera of libertarian paradise and paternalistic welfare state, bolstered by some ludicrous economic theories which are explained at excruciating length. There's even an appendix for those who haven't had enough of it. The basic premise of the theories is that the solution for all economic problems is for the government to print and give away money. Even liberals are more sophisticated than that.
Fortunately, Heinlein dropped this part of his philosophy while keeping its libertarian side. I believe a similar welfare state is portrayed in Beyond This Horizon, but I haven't read that book in three decades.
As with all his later works, Heinlein was taking a set of ideas and working out the effect on people of implementing them. He quickly learned how to do this while telling a good story.
Accurate prediction isn't the purpose of science fiction, but it is interesting to notice it when it happens. Some of Heinlein's hits include the ubiquity of television, TV preachers aiming for political power (Nehemiah Scudder makes his first appearance here), sexual freedom, the deification of Franklin D. Roosevelt, and an attack on Manhattan in 2003 (just two years off). He also has flying cars and no computers, but few writers of the thirties did better on those counts. We still have over eighty years to get the flying cars.
This is a book just for those readers who would automatically buy a new, previously unknown work by Heinlein. But they've already bought it anyway, without reading this review.
Note on dates: The book's publication date is given as 2004, even though it's still 2003 as I'm writing this review. Obviously Heinlein had one last time-travel trick up his sleeve.