I really don't know what to make of this book. I think a lot of reviewers did a better job at reviewing this book than I can.
To begin with, this book was a mixed bag. For I while, I would be angry with the book; however, doing a bit of research calmed my temper so I could attempt to understand what's going on. I understand now why this is a classic. While I was reading it, I felt I was reading something important, or at least deluding myself that I was. However, I can't put a finger on what the significance of this book is. To keep things short I'll bullet the problems with the book.

*Nondescript and strange future. The story is set in a future I can't figure out. It's far enough into the future for there to be flying cars, deep space travel, and other technology that I can really figure out. However, apparently basic civil rights has developed, women are still mainly consigned to birthing babies, being secretaries, and cooking. The problem I have with this is that the story is about the Man from Mars' reaction to human culture. If the setting is bizarre and strange for the reader, and the author throws on top of that the Man from Mars' confused and strange reaction, it just leaves everybody scratching their heads.

*Convoluted structure. This stretches from dialogue structure to the flow of the story. Heinlein seemed to forget the importance of signifying who's talking. I found myself reading section of conversation between a group of characters trying to figure out who's talking because that author would go for a page or more and have used the word "said" once. One particular flaw that I noticed was the ability of many of the characters to forget things, like Earth changing things. Example, Mike, the Man from Mars, demonstrates that he has the power to make objects and people vanish from existence and levitation. He shows this numiouers times and in front of some of the other main characters. However, later in the book when Mike demonstrates his powers again, the characters can't believe and believe it's a trick of some kind. Finally, the book itself is little more than a convoluted philosophical diatribe on various culture concepts such as money, possession, sex, and religion with a thin story wrapped around it.

One review said it best. This book reveals more about the time it was written than about the subject it's written about. It's an okay read, and will cause you to think, momentarily, about what makes us human and what builds and controls our civilization.