The novel started out pretty well. Heinlein was telling a story about a human that had been raised on Mars and learned a great deal from the Martians. I liked how the author was attempting to analyze human culture and attitudes via this alien lens that is the stranger in a strange land. But then the book veers towards the literary high brow and becomes the author's treatise on religion, politics, sex, commerce, you name it. The characters cease to be characters and become mouthpieces for what the author believes is wrong in contemporary (for the late 50s/early 60s anyway) American culture. As such we are treated with long passages of talking heads that espouse the author's viewpoints. At this point, I ceased to be engaged. I want a story, not a lecture.
Despite this complaint, I did find some of Heinlein's ideas interesting and some of them mildly offensive. Attitudes towards women are often sexist and was jarring to me. The idea of "Thou art God" I liked a lot, but then I tend toward the pluralist's view of religion as a whole.
As a side note, Heinlein originally wrote some 220,000 words for this novel, but his editors had him trim it down to about 160,000 words. The jury's still out if Heinlein's "author's cut" is any better, but I'd be interested to read reviews based on that edition. However, I'm glad I didn't have another 60K words to read.... Bottom line, read this book, as it is considered by many to be a classic, but don't be surprised if you're having a hard time finishing it.
Oh yeah, that's about the best thing I got out of this book, besides a new appreciation for the sculpture of Rodin -- the origin of the work "grok". It has been a part of software developers' lexicon for years. You can find it in the hackers dictionary.
The other interesting thing about this book was it's depiction of the technological wonders of the future. They got flying cars, but they don't got email or cel phones. Funny. Well, I guess these sci-fi writers can't see everything.