Cheliax, Empire of Devils is a solid entry in Paizo's line of Player's Companions for Pathfinder. The nation of Cheliax provides a far different feel than that of most fantasy, as it's a land where the rulers have openly made pacts with the devils! It's a dark and oppressive place to live, and one wrong word can bring the Inquisitors to one's door. I've read about several different areas in Golarion, and Cheliax is one of the most interesting and original. Cheliax, Empire of Devils contains the following:
* A map of the city of Westcrown on the inside front cover. The map isn't particularly good or detailed, and one doesn't see any cartographic talent at work.
* A twelve-page overview of Cheliax. This is one of those all-too rare occasions where the history of a fictional land is actually quite fascinating! This section a lot of useful information on the culture of Cheliax, as well as its leadership, perception of neighboring countries, organizations (such as the famous Hellknights), and even a few paragraphs on the arts scene(!). Some of this will naturally be more useful to GMs than players, but it was still done well.
* A two-page description of Egorian, a major city in Cheliax. There's a brief overview of the different districts of the town, but this was fairly bland.
* A two-page description of Westcrown, Cheliax's former capital before the pact with demons was made. As with the discussion of Egorian, there's not a lot of detail here and the material is probably of more interest to GMs.
* A section titled "Social" that contains brief one- or two-line descriptions of how the different core classes are perceived in Cheliax and then several new traits. This may be the most useful part of the book for PCs, and it's done well (if short).
* Four pages on "Magic & Spells", introducing several new magic items and spells. Good flavour links them to Cheliax.
* Two pages on "Faith." Purely descriptive, but good as far as it goes.
* "Combat", another two-page section. This is chock-full of feats, but contains an interesting sidebar on battle slang and one new weapon.
* Four NPCs detailed (with descriptions, pictures, and full stat blocks) in a "Persona" section. This would be really useful for a GM, but (apart from maybe integration into a backstory) of little value to players.
* The inside back cover has a map of Egorian. It's better than the map of Westcrown, but still falls a bit flat.
A word about the art: oddly, the cover art is much worse than the interior art! There's some absolutely gorgeous artwork inside (see pages 20 and 26 for examples).
Overall, this is another of Paizo's early entries in the Player's Companion line wherein they still hadn't found the right distinction between material for players and material for GMs. That being said, it's a good book and I'd recommend it.