For Us, The Living is Heinlein's first novel; however it is not his first story (that was an obscure story that has never been published), nor his first published work, nor even his first published novel. When it was first written no one would publish it -- in fact, it was never published while he was alive. This decision was made for good reasons. It is not so much a story as it is a series of essays on social and economic issues, and as a novel it is severely lacking. Despite this it is actually an interesting and potentially educating book, particularly if you are 18 and like radical ideas.
It is perhaps important to note that while it was (very lightly) edited and introduced by Spider Robinson, it is nothing like Variable Star, a later novel that was left unfinished at Heinlein's death and was thereafter substantially filled out and edited by Spider Robinson. FU,TL is published as purely a Heinlein work, and is unapologetic about being very bad. It is what it is, and if you don't like that, don't read it.
FU,TL was written sometime in the year 1938 or 1939, and as noted before, it is a pretty crappy piece when considered as a story. Even by 1939 standards, the writing is hokey and hackneyed, and by modern standards it's downright painful, being old-fashioned, sexist, and occasionally racist. Moreover, there is really very little story, most of it being a series of essays on society and economics. The narrative segments seem to have been added as breaks from the lectures, or as segues between talking points. Measured by plot and character development, this is not a novel but a brief novelette, which just happens to have been written in the margins of a lengthy political pamphlet.
As far as science fiction goes, Heinlein didn't do much; this is apparently on purpose, as one point that he wanted to make is that even in 1939, we had lots of cool technology that we didn't use, and that we could have the future here now if we would just get our act together. Televisions in every house, computers (in the sense of giant calculators), voice recognition/activation, all achievable in 1939! However, this level of technology is somewhat unimpressive in a story that is supposed to be set in 2086. The main technological advance in the 140 years covered by the story is that these inventions have moved from the laboratory and military use into the average home. Of course, there are flying cars and some technological innovations that reappear in his later works, such as the rolling roads. On the other hand, in 2086 we are only just starting to think of going to the moon, we still burn coal in the home for heat and energy, we use an extensive system of pneumatic tubes for the mail service, and we use the equivalent of a telegraph in much the same way as the internet functions today. To some extent, this remains a theme in all of Heinlein's later works; he can explain in great detail how a 1950s engineer could totally build a spaceship, but the next step in scientific advancement was often 'and then aliens show up'.
One of the primary topics of this book is economics. At this early point in his career, Heinlein believed that the best solution to a country's economic woes was to move completely away from the gold standard and allow the government complete control over the money supply -- to the extent of forbidding banks the right to lend on fractional reserves. He believed that unemployment and poverty resulted from the economy producing more goods than it was permitted to consume, and that for an economy to be healthy all goods produced had to be bought -- and if the consumers did not have enough money, the government should print and redistribute enough to correct this. His explanation of how this works is quite clever, and worth reading. There appears to be other economic hocus-pocus waiting in the wings that he did not get around to explaining in this book, for example, it is hinted that you automatically collect interest on money that you keep in your wallet, and that money depreciates automatically to account for inflation.
While this book does contain some political theory, Heinlein's libertarianism at this point is mostly limited to building a society in which victimless crimes are not crimes at all. This was of course a radical idea in 1939, and he was not shy in condemning religious mores and other social impositions on personal liberties. I am happy to report that there is not much sign of his 'dirty old man' period just yet, although he does include sexual mores in his critique, and is quite liberal in this area.
FU,TL introduces a number of ideas that reappear in later books: the aforementioned rolling roads, Nehemiah Scudder, Coventry, personalities jumping from one head into another, and, of course, touchy but friendly libertarians. While much of the same material reappears in his Future History stories, FU,TL is on a different timeline. As Heinlein gave up on having it ever published, there is no attempt at consistency with any of his other works.
This book does contain some unique ideas, and it is quite readable -- as long as you aren't looking for an exciting story. Heinlein is pretty smart, and even his old ideas are interesting, even after 70 years. However, it really isn't much of a story, and I wouldn't recommend reading it just because you are a Heinlein fan, unless you are interested in it out of historical value. This is a fun book to read if you want to hear some essays on radical ideas that, amazingly, remain new and original even today. It will not change the world, nor impress the trained philosophers and economists among us, but it will give you some things to think about.