The biggest problem I had with Robert Heinlein's Stranger in a Strange Land was that it felt very much like two novels slammed together in a desperate attempt to form a singular work. There is a very definite shift in the last quarter of the novel, where the consequences of characters' actions begin to vary wildly from expectations. None of this would be problematic if the first three quarters of the novel had not been spent criticizing what the final quarter ends up promoting. Specifically, the shift in portrayals of religion in the novel is sloppy and poorly executed. Heinlein attempts to justify his sudden promotion of institutionalized religious dogma by explaining that he does not consider Valentine Michael Smith's church to be a true religion as much as it is a spiritual movement. Yet he goes to great pains throughout the novel to draw explicit parallels between Mike's church and that of the Fosterites, as well as to paint Foster himself as a huckster, only to suddenly reverse himself on both counts at the end of his story.
Worse, Heinlein's shifts his writing style in the latter sections of the novel and commits the greatest sin a writer can commit: he starts telling us what is happening, rather than showing us. We hear a lot about Mike's church and its impact on society and the way people react to it, but we don't actually see any of this until the end, at which point it lacks the necessary emotional context to have a great impact. In addition, he begins to introduce new characters while downplaying established ones, to the determent of the story as a whole. The character of Jill, for instance, ultimately is a non-entity by the end of the story, despite being crucially important for the first three quarters. Did he stop liking her? Did he just not want to write her anymore? Why does he forget her so quickly?
Additionally, Heinlein's theme has shifted profoundly by the end of the story. Initially promoting scientific reason, skepticism, and the foolishness of human culture, law, and institutions, he changes his tune and instead chooses to promote vague spiritualism and a survival-of-the-fittest mentality the belies not only previously developed ideas, but also the hitherto established Martian social structures which Mike's character values. In the end, Heinlein tells us his message, but the way that it clashes with the themes developed throughout the story uncut its effectiveness.
I am being critical, I know, and I would recommend the book to anyone with an interest in science fiction. In the end, though, I couldn't enjoy it on the same level I could some other sci-fi classics. It is guilty of too many of the things that it criticizes, and by its end, Heinlein has done what I considered impossible for him: he has stopped writing to the best of his abilities. That alone makes this novel a tragedy.