This is undoubtedly one of Heinlein's finest 'juvenile' novels (and anyone who thinks there were no female characters in it must not have read more than 10% of it).
I usually list _Tunnel in the Sky_ as my favorite of Heinlein's young-adult novels of the 1950s, and I still think it belongs at the top of the list. But this one is very close.
As I'm sure you know already, it's the tale of a young fellow named Thorby, a slave on the planet Sargon who comes under the protection of one Baslim the Cripple. A sort of outer-space version of Kipling's _Kim_, the novel traces Thorby's life and development through several changes of venue -- and ends on Earth, where Thorby finds out who he really is and takes on some heavy, adult-sized responsibilities.
It's a very well handled coming-of-age novel, and it expresses Heinlein's own remarkable take on maturity very nearly as well as _Tunnel_ (in some ways arguably better). And like _Tunnel_, it devotes _just a little_ space, toward the end, to preaching against straw men. (Here, it's a couple of custard-headed pacifists whose sole literary function is to mouth inane slogans that Heinlein wants to show up as irresponsible nonsense. There was _loads_ of such stuff in _Starship Troopers_ but in this one it's kept to a minimum.)
It also shares part of its 'skeleton' with _Stranger in a Strange Land_ (on which Heinlein was also working at about the same time, still under its provisional title 'A Martian Named Smith'). Why, there's even a climactic courtroom battle, with Thorby represented by a crusty lawyer not terribly unlike Jubal Harshaw. (In general lawyers don't come off well in Heinlein's novels; in the final analysis the sharklike Garsch is no exception, although Harshaw fares somewhat better.)
At any rate, the anthropological insights come fast and furious here (aided in part by a character who may remind you of Margaret Mead). One nice touch is revealed in Thorby's time with the Traders; like every other people in history, they call themselves 'the People' and everybody else subhuman ('fraki').
No s-e-x, though. At this time Heinlein was still publishing under the watchful eye of Alice Dalgliesh and Thorby's interactions with the opposite camp are as chaste as melting snow.
I credit Heinlein with three absolutely magisterial works -- _The Moon is a Harsh Mistress_, _Double Star_, and _The Door into Summer_. This one belongs to the second tier of near-magisterial material, well worth reading and rereading despite a few warts.