It's actually about dragons throughout Eberron in general, but it does include a first real look at Argonnessen as a whole continent and the culture of the dragons that reside there. A brief history of dragons and some key historical events is included as well as the theology of the dragons, which was a fantastic read.
On the whole, it really gives a strong insight to the bigger picture of Eberron and its mystical nature. You also get a much stronger feel of how to use dragons in Eberron. All of this targets the book to being about epic-level campaign ideas, too.
Honestly, if I hadn't moved and was able to continue my dragon-themed Eberron campaign, which started with Eyes of the Lich Queen, it would have been of great use, but unfortunately, the new player in my new campaign aren't interested in a dragon-themed campaign.