I really enjoyed this Pathfinder supplement. The TL;DR is that it's technically sound, inventive in it's augmentation of the mechanics, and if you love dragons this feels like a love letter to them.
When it comes to the fundamentals, it's got the bases covered. It's a well formatted document that follows all of Paizo's standard organization, headings, etc. which makes it very easy to follow as a reference document. Additionally, it makes great use of Paizo's freely available art under the OGL (thanks Paizo!) so it feels right at home in my Pathfinder collection. It's also clear that the author is very familiar with the Pathfinder ruleset, and Paizo's standard conventions, and everything feels very well balanced and not over or under powered.
Getting into the meat of the document, it's got a lot of fun additions to any character or campaign where you want a little extra dragon flavor. I'm really bad at coming up with Backgrounds on the fly, so it's really nice to have plenty of options which this doc gives. There's also a lot of class mods that are all great. I especially liked the Research Field for the Dragon chemist which I think has a very inventive use of breath weapons. It's so thorough that when I thought to myself, "No Dragon themed cavalier?" I had to quickly pull up the pfsrd to find out that there already was one I had forgotten about! There's also a lot of great little flavor additions like spells, and modifications to the Riding Drake from the APG to round it out.
Long story short(er) this is a great supplement that is a must have for any dragon focused campaign or character. After reading through it I have a bunch of great ideas for characters and I can't wait to use it in a campaign. Well worth the $3!