These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Stranger in a Strange Land
Anvilicious: In case you didn't get it, Robert Heinlein dislikes mainstream religion (particularly televangelists), likes polyamory and also likes "pleasantly plump" women.
He also advocates personal development (in a semi-spiritual sense). In this book, if your mind and spirit have been trained, you get to have superpowers.
Mike fulfills most of the Marty Stu requirements, including being Too Good for This Sinful Earth... but fails the primary one because he's not a Self Insert. From one perspective the book is not about Mike, but about a world of ordinary people who have to cope with the fact that a Mary Sue not only exists, but is giving "Mary Sue lessons."
Jubal Harshaw is a "LL.B., M.D., Sc.D., bon vivant, gourmet, sybarite, popular author extraordinary, neo-pessimist philosopher, devout agnostic, professional clown, amateur subversive, and parasite by choice." Yes, that's three doctorates. He is also incredibly wealthy, does little real work and keeps a harem of sexy secretaries. Oh, did we mention he just happens to be the Author Avatar?
Although, based on some more offhand comments, it's implied that the requirement for doctorates has become lower, rather than Jubal being exceptionally smart to get them.
A possible lampshade hanging shows up in a single line.
Ben: Jubal, you have troubles? I thought you were the one man who managed to beat the game.
Nightmare Fuel: Valentine Michael Smith has vast psychic abilities owing to his Martian upbringing. Among these is the ability to make any object, regardless of size or make-up, just "go away." This includes humans, and Smith spends most of the book with an odd mix of Blue and Orange Morality and Black and White Morality, meaning if he perceives a "wrongness" in you, you're just gone. Mike's bodycount, not that there are any bodies to count, gets up into the high hundreds.
As Jubal points out in the book, the moral code that religions always ascribe to their gods is not the same as that they insist on for mortals, and this combines in disquieting ways with Mike's philosophy that all people are God.
There is a second and more deliberate Nightmare Fuel in the notion that the "Old Ones" of Mars are capable of dismantling planets, have done it in the past, and simply haven't made up their minds yet on whether or not to do it to Earth.
Seinfeld Is Unfunny: This book wasn't written to exploit the counterculture movement of the 1960's, but predicted it. Since then, free love has become significantly less shocking and controversial (although something of a Dead Horse Trope).
However, Heinlein's publisher pulled it off his "too controversial to print" list and released it to exploit the counter culture movement of the 1960s.
Values Dissonance: Jill's ideas on women, homosexuality, and sexism are frighteningly reactionary for such an otherwise progressive book. Her Character Development consists largely of the more liberal Jubal (and especially Mike) getting her to recognize this and become less prudish. Duke undergoes a similar, if abbreviated arc, and the main conflict of the story is Mike's "church" running headlong into the reactionary values of society.
All of the male characters, even Jubal, talk patronizingly to Jill and the other female characters, and love to lecture them about why they're wrong. Note that Miriam is a scientist and Anne is a Fair Witness (a completely unbiased legal expert).
Spanking is mentioned or brought up with what Adam Cadre called a "what the fuck is your problem" frequency, which doesn't jibe well with the misogynist tendencies described above.