So it seems Heinlein attempted to write "young adult" (or possibly what the book industry is now calling "new adult") fiction. Our main protagonist, the cheerfully ambitious and optimistic Podkayne Fries, is on her first journey to another planet, leaving her home planet of Mars with her politician uncle and her brilliant yet likely psychopathic little brother. Shenanigans happen, with a not exactly happy ending, but then again, Heinlein has left his novels with ambiguous endings.
Now, Heinlein passed away some years ago, and even if he hadn't the words of my review wouldn't be of any consequence to him. But I really feel he had no business trying to write a teenage girl (or even a teenage boy, though we have limited experiences with Clark). There are a few parts where I feel he did actually manage to hit a decent voice (largely in terms of the self-absorption we all tend to go through during those years), but largely Poddy was painfully unbelievable as a cusp of adulthood girl.
Perhaps part of the younger reading group, Podkayne of Mars lacks much of the standard political, economic, and moral discourse present in other works by Heinlein. The discourse still exists, but written in a much lighter hand than normal. As someone who is familiar with a range of Heinlein titles the lack of sexual content was almost shocking, however I don't mind the lack of incest (even with his justifications it still makes me go "ew").
The ending of the book is the most interesting part, and perhaps where we learn that the story might not really be about Podkayne so much as it really is about her brother and humanity. The book actually has two endings, the one Heinlein originally wrote, and the one that the publisher essentially demanded. The version of the book I had contained both endings so I was able to compare them. Both endings have power, but it is Clark's introspection that I really like out of the modified ending.