This is the first science fiction book I liked (before that I had read the time machine and the war of the worlds).
The plot is easy enough: Earth is overcrowded, new colonies are being stablished in Ganimede. The hero decides to go there with his newly married father and his step mother and sister. Once there, they'll have to take part in the post terraforming effort, and become farmers much in the old colonial style. They suffer from earthquake (can you use that word?) and several other penalties, and in the end they become true human beings.
For the modern reader, Heinlein's rethoric, full of outfashioned machismo, matter-of-fact virility, easigoing logic about life and existence seems outdated and even sounds sarcastic. The hero rules his world by his boy scout code, and all the characters shape reality with perjudice rather than mentality or ideas. I rather liked it as a teenager, everything seemed so easy (quote "survivors survive")
However... the book is very well written, action soars, situations are superbly described, one wishes the author had some more ideas about places or adventures for the hero. He does not refuse to write nasty things when he has to: future is not that nice, even in this pack of healthy pioneers you can find some samples of the stupid, the corrupt, the inept who make community life a headache.
So... for me this is Heinlein at his best: full of life, action, enthusiasm about mankind and the possibilities - and limiations - of our race . It should go with "The puppet masters" and even that undercover fascist manifesto "Starship troopers".
Enjoy a shake!