The Companion line is supposed to present a player-friendly product to help in creating characters from particular regions/races/religions/whatever. I bought the Dragon Empires Primer (DEP) for this very reason, thinking that it would be just as useful as the Inner Sea Primer (ISP).
Well, the Dragon Empires Primer certainly is similar to the Inner Sea Primer. They both have short-but-interesting half-page summaries for each country in the region covered, and a couple of pages each on archetypes (DEP has lotus geisha bard, sword saint samurai, white-haired witch, and yokai hunter ranger), arcane spellcaster variations (DEP has the oni bloodline and the void elemental wizard school), and major deities and other religions/philosophies.
The DEP has two more pages devoted to races than the ISP (which has only two). That is not surprising, as five new PC-playable races have been introduced along with a multitude of Tian ethnicities. There are also three kitsune racial feats plus a double hand-full of combat-related feats.
Unlike the ISP, the DEP does not have an abbreviated time-line to bring players up to speed on both the broad strokes of history (Earthfall/Age of Darkness, other Ages, etc.) and some of the most recent current events.
Also unlike the ISP, the DEP has two pages devoted to honour in the region, its importance, and how to track it. The system is similar to the Reputation system for the Land of the Linnorm Kings (Campaign Setting sourcebook).
The problems ...
Mistakes in the crunch/rules-heavy part. Examples include the oni bloodline's class skill, a spell name changed between a school spell list and the actual spell write-up (the same spell also has an error), and an error relating to the sword saint archetype's brutal slash class feature.
Lack of one very important player aid when creating a character - deity domains (and sub-domains). Something like that is easily left out of the ISP because those same deities are also in the Core Rules (which presumably a player has access to when creating a character). But what about a player making a character for/from the Dragon Empires?!? Most of those deities' domains are not listed in the Core Rules (exceptions: Abadar, Desna, Irori, Lamashtu, Pharasma, and Shelyn - which leaves 14 others).
Quite honestly, I think that the DEP should have used one page for listing the domains of the deities worshipped in the Dragon Empires, and one page for describing the importance of honour in the region. (While putting this information in the player-friendly sourcebook is probably a good "heads up" for players, the actual rules relating to honour should have been put in the Gazetteer.)
The lack of an abbreviated time-line also irritated me. I'm still not sure which are the 16 Successor States, and I won't know unless I do some careful reading of the 28 individual country write-ups.