Robert Heinlein is my favorite of the Big Three of Science Fiction
(Assimov/Clarke/Heinlein), simply because I think he tells better stories and is more proficient at creating interesting characters (yes yes, YMMV!).
Stranger in a Strange Land is Heinlein at his best, creative, provocative and controversial. I may not necessarily agree with the ideas and philosophy put forward in this book but I had a blast reading about them. The protagonist Michael Valentine Smith
with his weird ideas and psychic powers may be focus that drive the entire novel but his adopted father Jubal Harshaw
is the standout character for me, the one that stays with me to this day. I just love the way he pontificates, nobody write pontifications like Heinlein! This is one of those rare sf books that "mainstream" readers deigned to read in droves, most of them probably never understanding its value as sf or gain a lasting appreciation of the genre.
In any case this book needs to be read not because it is a classic, but 'cos it's like far out and groovy man!
Read it, grok