About the gods: Walton is careful to point out that the gods of many religions are real in the world of The Just City. Apollo and Athene are from the Greek pantheon, but he specifically describes others such as Jesus as being real also. There's a single all-powerful Father that is above them all, who is a mystery as much to the gods as to humans. It's an interesting way of using gods as characters while mostly removing religion from consideration.
I vaguely remember discussing Plato's Republic in school many years ago, as one among many philosophical works. The details are hazy, though, so I'm glad Walton generally explains what is being attempted, rather than assuming you know the source material. I'm sure there are some subtleties that I missed by not knowing the Republic in great detail, but the book is certainly accessible with only a vague understanding of what Plato wrote.
The Just City documents what happens when you try to implement a thought experiment in reality. Unsurprisingly, there is a lot of compromise involved, and some parts don't work as well as one might hope. The masters are all believers in the Platonic ideal at first - they were chosen specifically for their desire to be in such a city - but as time passes some of that certainty fades. The children are raised in the city and for the most part accept it as natural, but over time it becomes clear that human nature just doesn't line up with some facets of the ideal. Most notably, the elimination of marriage in favor of a randomized "festival" to pair up the "best" parents causes serious discord.
From a character standpoint, I thought Walton did a fine job in giving the reader relatable individuals to follow. The majority of the book follows three: Apollo, who has taken the form of one of the children; Maia, one of the masters; and Simmea, a child brought to the city from her former life as a slave. Each of these is well developed and understandable, and many other characters make extensive appearances. Chief among those others is Sokrates, who was brought to the city by Athene to teach rhetoric and debate. His constant questioning and argument is a major factor in the eventual fate of the experiment.
There's not a lot of physical action or conflict in The Just City, but plenty of philosophical discussion and struggle with how to reconcile reality with ideals. Equality of the sexes is a basic tenet of the Republic, but is still a struggle (particularly among the masters from older historical periods), both socially and in terms of physical assault. The nature of the gods as powerful but flawed, especially when it comes to taking into account the will of anyone else, is a key theme. Slavery is generally considered unjust and undesirable, but still used as a tool on some occasions. These and other themes, along with interest in the viewpoint characters, kept my attention throughout the story.
Even if the ancient philosophy represented by Plato's Republic isn't particularly appealing, The Just City has plenty to offer. The interactions between the characters and the process of building the city have plenty of entertainment value. I think most readers will find the philosophical discussions interesting as well, as they fit nicely into the flow of the book.
