Scavenger Sons is basically the foundation of Exalted, or at least it was until third edition came out. The beginning of the book explains that the countries and places covered inside aren't a random sample, but are biased in favor of "less-civilized" areas and places where the Realm doesn't cover. In other words, places that it's more likely that the Solar Exalted would be from. First edition spent some time filling these places in, and then second edition, by editorial directive, almost never spent any time on places that hadn't been covered already in the line. The first time Exalted got a large number of new locations covered after this book was in Masters of Jade, over a decade later.
As I read, I noticed how much it was obvious that the map of Creation had been expanded in the middle of working on the line. All those national relationships in the Exalted corebook that make no sense because of the distances involved were first on display here. Sijan getting food from Nexus even though it's hundreds of miles away. The Halta vs. Linowan war. The Coral Archipelago being described as near the western shore of the Realm where near means "two thousand miles of open ocean." Greyfalls being a Realm tributary even though it's a year round-trip. A trade war between Paragon and Gem, which are separated by over a thousand miles of trackless desert.
As problems go, that is a large one, but it's nearly the only one the book has. People on the internet tend to say that the draw of Exalted is its setting, and other than the final chapter, this book is entirely setting. There are six chapters of it, one each for the four cardinal directions, one for the Scavenger Lands, and one for the city of Nexus, which is clearly being set up as the kind of anarchic area where the rule of law runs thin and thus adventurers--or Exalted--can find a place without having to deal with the heavy hand of the authorities.
The best parts are the ways that the book tries to make Creation's cultures realistic, or realistic reflecting a world of active spirits, supernatural beings, and pervasive magic. Like Skullstone, the capital city of Onyx and part of a shadowland ruled by the Bodhisattva Anointed by Dark Water. You might think that would be an unattractive place to live, but immigration is high because the walking dead do most of the work, and in a iron-age society, having almost all manual labor done by animated corpses who do not feel fatigue or pain and is a huge draw. Meanwhile the city of Great Forks is a slave economy, with slaves outnumbering citizens 2-to-1, but slaves are often kept drugged with a leaf that causes memory loss and euphoria, so they chew it, work all day, and "wake up" at the end of the day. Or going slightly more further afield, the way that the city of Whitewall made a treaty with the nearby fair folk and dead so that they can't enter the city without invitation and can't attack anyone on the road. As such, the city has a huge population because of all the farmers, miners, and workers who can't live outside the walls, and the buildings inside are all stark and devoid of ornamentation, since everyone spends all their time indoors to avoid both the cold and any monsters who manage to get into the city. And the similar treaty in Halta, where the Haltans live in the trees, the fair folk live on the ground, and anyone who ends up on the ground is fair game to them.
Or how in Nexus, there are several tombs of the Solar Anathema. One of these burns white-hot, enough to carbonize flesh with a single touch, and as humans do, the people of Nexus have found a way to use this--they covered it in bricks and built an iron foundry around it to have an eternal, free source of heat. I like that depiction of the magical and the mundane side-by-side.
There's a lot in this book that I forgot over the years, like how Greyfalls is ruled by the Nuri, who fled Wyld barbarians and were an oppressed minority until the Realm showed up and put them in charge, as has been the tactic of colonial powers for time out of mind. Or the gambling house in the Coral Archipelago with First Age artifacts that allow the betting of intangible concepts, so rich, elderly merchants will bet vast sums of money against the youth of a beggar boy. Or the frozen fog in the north, blown in from the Wyld, that can freeze someone solid in moments.
I could really just keep listing bits I liked for a while, but in the interests of space I'll move on.
Even after all that, one of my favorite parts of the book is the end section on the fair folk. I can appreciate that Exalted: The Fair Folk is a well-written, mechanically-tight work, but I never liked "Rakshastan" or the idea of the faerie as creatures of dreams rather than creatures who needed dreams to live. In Scavenger Sons, the fair folk take on shape flavored by he element strong in the part of Creation where they entered from the Wyld, and so their powers are elemental- and mentally-based. There's a description of what would become shaping combat, but no emphasis or rules for it. Basically, I don't like what happened to fair folk when they became playable, and I really don't like the idea that fair folk are living stories who know they're in an RPG and are just trolling everyone else for the lulz because I think it does almost irreparable harm to the themes of the game. The faerie as beings of pure chaos who take on shape because they have to to survive the relentless erosion of Creation, rather than because it's part of some story they're telling themselves? I'm there for that.
Even now, Scavenger Sons is probably the best setting book for Exalted. It does in one book what it took second edition five books to do, with more of a feeling of mystery and a more interesting world. Even if you're playing 2e, use this for background