If you don't buy it for anything else as a DM: it has the actual sizes for dragons. None of this Small, Medium, Large crap: actual sizes in feet for all aspects of the dragons (neck, body, wingspan, etc.) and their weights. I'm so happy with this book!!! Plus the hoard write-ups are greatness.
I really like the book. There are many good points about the product, and fewer bad points. I think it mixes the material well in general. I am pleased with my purchase, and consider it to be the best 3.5 product I have at this point. As an aside, artwork is one of my considerations as well when purchasing rpg material, and this one did not disappoint me.
I love dragons, so I'm biased. However, there's quite a lot of stuff in here - ways of making distinctive hoards, new spells, what have you - that isn't dragon-oriented, strictly speaking, and really, who wouldn't want to run a dragon-centric campaign after going over all this?