Dwarves of Golarion is one of the earlier entries in the Pathfinder Player's Companion line, and the first book dedicated to a specific race. The artwork, though serviceable, is clearly inferior to the current Paizo standard. The inside front cover of the book has a nice, full-page summary of Dwarf racial traits and a list of dwarven gods, while the inside back cover has a map of the Five Kings Mountain region that is rather-well detailed, containing over two-dozen settlements, fortresses, and mines. The 32 pages of the interior are divided into the following sections:
1. "Dwarves of Golarion" (10 pages): An introduction and overview to Dwarven physical, mental, and cultural norms. Everything from Dwarven diet to Dwarven fashion is covered here. Frankly, there's little that strays from the stereotypical fantasy notion of a dwarf, and players experienced with previous versions of D&D will find most of their preconceptions confirmed. There are a few pages on Golarion-specific history of the Dwarves which is reasonably interesting--events like the Quest for the Sky and places like the Sky Citadels offer some insight into Dwarven culture.
2. "Dwarven Character Traits" (1 1/2 pages): This section introduces eight race traits, six religion traits, six regional traits, and four magic traits. The traits are flavourful and tie in well to Golarion's conception of dwarves. Mechanically, they are certainly not game-breaking and for the most part rather bland in effect.
3. "The Five Kings Mountains" (8 pages): This is a gazetteer of the Five Kings Mountains, the center of Dwarven culture in known Golarion. Several major cities like Larrad, Highhelm, Kovlar, Rolgrimmdur, Taggoret, and Tar-Kazmukh receive at least a couple of paragraphs each. Other topics include natural hazards and foreign relations. Four pages of this section are actually about other Dwarven enclaves beyond the Five Kings Mountains, and cover the Darklands, Kalsgard, the Kodar Mountains, the Mindspin Mountains, the Shattered Range, and Osirion. This section would be extremely useful for GMs planning to run Dwarf-centered adventures in any of these locations. My guess is that most players probably don't need so much information and will just skim it.
4. "Combat" (2 pages): There's a brief, non-mechanical but flavourful description of legendary Dwarven combat tactics to start this section. Next, five Dwarven combat feats are covered and a new Dwarven weapon (the Dorn-Dergar) is introduced. The feats are really fun! If I had a Dwarf PC, I could definitely imagine taking some of them like Bounding Hammer or Sliding Axe Throw, as they have a nice Dwarf-specific flavour and would be effective in combat.
5. "Faith" (2 pages): This section is almost entirely new spells. Nine new spells are introduced, and all of them are divine spells for clerics, rangers, and paladins. An odd mechanic is set forth that limits these spells to worshippers of particular Dwarven deities unless a special ritual prayer is said.
6. "Magic" (2 pages): Three spells relating to veneration of one's ancestors are introduced for Dwarven clerics and bards only. There's one new spell for Dwarven rangers & druids and two new rune-focussed spells for sorcerors and wizards.
7. "Persona" (4 pages): Three NPCs are given full stat blocks and descriptions. I still don't really see the value of including NPCs like this in a Player's Companion, but it has potential value for GMs who buy the book and need to provide a contact, a cohort, etc. There's also a one-page overview of Dwarven deities, each of whom only has a paragraph or so. I'm not sure why this wasn't placed in the "Faith" section, and the description of each is quite cursory.
8. "Social" (2 pages): Three topics--Dwarven beards, ales, and craftsmanship--are discussed. Definitely not essential, but could be good for players wanting to add a little more flavour to their PCs. A couple of the ales even provide alchemical bonuses for an hour or so, an idea which I can safely say I've never seen before.
Overall, there's not a lot in this book that is especially memorable or innovative. A player with this book and a player without this book would probably portray Dwarves in Golarion equally well, especially now that the feats and spells would be available on various websites. If anything, I'd recommend this book more to GMs who need a relatively quick overview of Dwarven history in Golarion and the Five Kings Mountains for a campaign set in the area.