Robert Anson Heinlein was one of the great the Big Three sciene writers of the Golden age of Science Fiction in the middle 20th century,
together with Isaac Asimvo and Arther C. Clarke.
Though he appreciated the romantic adventurous sci fi of the early 20th century that introduced him to the genre, his own writings stressed scientific accuracy, pioneering true, hard core 'speculative fiction' (Heinlein's own terminology). He used his intelligence and wit to come up with many novel ideas, like planet-bombing rock throwers, self-moving roads, time loops where cause and consequence form circles, and many more. He is credited with envisioning waterbeds, mobile phones and the internet, all well before they actually came into being. He was a great supporter of the space industry, even when it did not yet exist, describing space travel and everything that comes with it in quite realistic terms. And even when he moved to the far fiction end of the science - fiction scale, he was imaginative. From The Number of the Beast:
"Sharpie, can you explain precession in gyroscopes?"
"Well, maybe. Physics One was required but that was a long time ago. Push a gyroscope and it doesn't go the way you expect, but ninety degrees from that direction so that the push lines up with the spin. Like this --" I pointed a forefinger like a little boy going: "Bang! -- you're dead!" "My thumb is the axis, my forefinger represents the push, the other fingers show the rotation."
"Go to the head of the class. Now -- think hard! -- suppose we put a gyroscope in a frame, then impress equal forces at all three spatial coordinates at once; what would it do?"
I tried to visualize it.
"I think it would either faint or drop dead."
"A good first hypothesis. According to Jake, it disappears."
Heinlein did not limit his writing to scientific fiction. He was well aware of the influence of the world around us on humanity and explored that field thoroughly, expressing his own political, religious, sexual and cultural views in his stories. As he was rather nonconformist, leaning towards both libertarianism and fascism at the same time, this made him a controversial writer. It also made him go beyond the science fiction fans and draw the attention of mainstream readers. From The Moon is a Harsh Mistress:
"I will accept any rules that you feel necessary to your freedom. I am free, no matter what rules surround me. If I find them tolerable, I tolerate them; if I find them too obnoxious, I break them. I am free because I know that I alone am morally responsible for everything I do."
Early in his career Heinlein wrote several 'juvenile' novels, targeted towards young adults.
Later he broke into mainstraim publishing with controversial works, which include some of his most famous books
like "Starship Troopers", "Stranger in a Strange Land" and "The Moon Is a Harsh Mistress".
Heinlein's style of writing can be tiresome, with many lines filled with babble among his characters. Intelligent talk, often contributing to the storyline, but wearing babble nonetheless. This style of writing expanded in his later works. Still, hidden among all those words there are always interesting ideas and viewpoints. Maybe Heinlein was not so adept at saying things as some silken smooth writers, but he had more to say than many of those. From Solution Unsatisfactory:
"The trouble with you youngsters," Joe said, "is that if you can't understand a thing right off, you think it can't be true. The trouble with your elders is, anything they didn't understand they reinterpreted to mean something else and then thought they understood it. None of you has tried believing clear words the way they were written and then tried to understand them on that basis. Oh, no, you're all too bloody smart for that, 'if you can't see it right off, it ain't so' it must mean something different."
Heinlein remains a controversial writer, even several decades after his death. Most people either love his writings or hate them, though their complexity demands a more nuanced view. If you want to grok Heinlein, it is probably best to follow his writings chronologically. Start with short stories like "By his Bootstraps" and juvenile novels like "Time for the Stars", then work your way up through the social novels to his later novels.
I think that science fiction, even the corniest of it, even the most outlandish of it, no matter how badly it's written, has a distinct therapeutic value because all of it has as its primary postulate that the world does change. I cannot overemphasize the importance of that idea.
Read more at https://www.heinleinsociety.org/.