Nice depth of content.
If you add up all of the PHB pages dedicated to race, you get 25 pages across 9 races. And those PHB pages are heavy in pictures. This one is about a dozen pages for 4 races (Hagborn, Samsaran, Tengu and Catfolk). With limited art, there is a serious amount of content here.
I really love the core structure of how the races are detailed. Each race has sections like "Love & Mating", "Alignment & Religion", "Clans & Families" and "Aging & Death". These are all thought through quite carefully, the races go well beyond just a simple stats list.
From a design side, all of the races are reasonable and seem pretty balanced. The Catfolk grant +2/+2 instead of the usual +2/+1, which is a little odd, but the overall design is still solid.
There are some extra sub-races at the end, but these are really just a bonus. The list price is worth the while.
The key spots for future are the one that are hard to do on a small budget. More artwork would definitely be nice, especially for the Catfolk where the two distinct sub-races look very different but we only have a picture of one. The book could also really use a designer's touch. Page numbers are hard to read. The core racial stats are "cut into" the descriptive text about each race, so you have two columns bleeding into one column without so much as a horizontal rule to cut them up. The text is all straight black, no color variation, almost no font variation, it's all a little hard on the eyes.
Overall though, I'm impressed. There are lots of "freebie" races out in the wilds of the internet, but very few of them have as much detail as these ones.