First, on the planet Charity, the crew encounters intelligent centaur beings leading around ugly humanoid slaves as food stock. Is it just me, or is this an homage to the Houyhnhnms and Yahoos of GULLIVER'S TRAVELS (a book I suspect the author liked very much: STRANGE IN A STRANGE LAND is something rather Swiftian)?
Second, the hints dropped that Starman Jones lives in a repressive Imperium, complete with ranks of nobles and underlings, guild rules, restrictions on trade and profession--all that simply went over my simple head as a twelve-year-old.
But the theme, and how it is handled, is actually rather mature, rather conservative in character. The hero cheats the system, and enters the Chartsman's Guild on forged papers; but, before the end of the book comes clean, turns himself in, and pays a huge fine. The book emphasizes a middle path between the extremes of always obeying the law, just or unjust, and the anarchy of always thinking the rules are meant for everyone else but you. It sounds like the kind of thing one comes across in the service: you cannot obey the rulebook in every case, but you cannot throw the rulebook away.
Sam, the heroes mentor, is explicitly a relativist: he saws the moral rules vary according to time and circumstance. This theme is a common one in any Heinlein book. However, unlike his adult books the relativism here is questioned and rejected by the painfully honest main character. In some ways, Heinlein's juveniles are more adult than his adult books. (Relativism is a teen philosophy, after all.)
The description of Nova Terra, the planet to which Jones and his mentor Sam head, sounds like the American Frontier of the time of Daniel Boone. A man can light out for the horizon with an axe on his shoulder, cut himself a log cabin, hunt and trap and farm the land, with no leave nor let asked of anybody. The main appeal is the lack of regulation, the lack of taxes, the lack of these very rules that make life on Imperial Earth oppressive. The author does not say so explicitly, but from hints in other books (STARSHIP TROOPERS comes to mind) I suspect Heinlein's idea is that regulation is due to population, and over-regulation due to over-population. On a colonial planet (as in early America) the value of labor was high, because the number of workingmen was low: a philosophical and social system which placed high value on the individual was the result.
Third, the hero does not get the girl. Jones becomes an Astrogator at the end of the tale, and the girl marries someone else, a fiancee picked out by her father: he takes this stoically, thinking that Astrogators should not get married. They are wed to their starships!
Fourth, little anachronisms crop up. The main talent of the hero is that he has memorized the log tables of the astrogator's manuals, so that, when the starship is approaching the mathematically complex transition through hyperspace, and the navigation officers GET OUT THEIR SLIDERULES and solve the problems to be fed into the computer IN BINARY CODE, Jones is the only one who can do it in an emergency. The technical capacities of Imperial Earth do not extend to making an adding machine that can punch the binary equivalent of decimal numerals. They cannot make a type-writer with a 2 on the key and a 10 on the punch.
Another thing that struck me as odd, was that the Jones house had no running water. He lived on a farm, so he pumped wellwater into a bucket for cooking. Part of this is meant to show his poverty: Jones also has to chop wood to burn in a broken electric stove. But part of this, I assume, was that the penniless hillbilly was a more common stock character back in the 1950's. Not everyone had running water.
Fifth, the deceptively simple prose, the uncomplicated structure of the narrative, makes for an easy read, but the effects on the reader's emotions shows great craft. And this was merely one book of a dozen Heinlein turned out of like quality on a routine basis.
Overall, it is a well done book, and surprisingly deep for a kid's book. No wonder Heinlein is called the Dean of SF. He merits the title.