Fortunately, I was not disappointed.
The Runaway Robot says "by Lester Del Rey" on the cover, but in actuality Del Rey only did an outline; the actual novel was written by Paul W. Fairman, and is undoubtedly the best-known and longest lived of his works (although a couple of his other stories inspired some old pulp-sf style movies).
The action takes place in a world that is clearly a classic 1950s-60s "far future" reminiscent in many ways of some of Heinlein's juveniles. Interestingly, the changes in culture since the time it was written may, in some ways, have improved the novel; the culture of 1960-imagined-future is similar enough to recognize, yet alien enough to feel like something not quite of THIS world, especially for young people today who weren't living during the 60s and 70s.
The story is fairly straightforward, as befits a juvenile novel. Without giving away too many details, the viewpoint character Rex is a robot, a manufactured companion, caretaker, etc., for a boy named Paul, son of the mayor of a small city on Ganymede. When Paul's family is suddenly recalled to Earth, the company employing Paul's father won't pay to ship a robot across the Solar System, and so Rex is sold off. But neither Paul nor Rex is happy with this arrangement, and the novel follows their determined struggle to stay together, and especially Rex's struggle with the limitations of being a mere robot in a world dominated by human beings.
It's a pretty tightly plotted, well-told yarn, with lots of influence from the classic pulps (lots of native-to-the-solar-system races like Martians and Venusians, etc.) and a couple of very interesting twists thrown in to make it not just the Same Old Thing. Rex is a fun character to spend a book with, self-deprecating, honest, puzzled by the world around him, and perhaps just a bit too humble for his own good sometimes. There's real struggle and a number of true moral conflicts and dilemmas that both Paul and Rex have to face before reaching the conclusion of their journey.
I strongly recommend this wonderful, if somewhat dated, novel to anyone with kids of the appropriate age. I had a lot of fun re-reading it, too.