Outbreak: Undead is in my opinion the best zombie game available, and Outbreak: Wild Kingdom is a suitably high-quality supplement for it.
Quite frankly, if you're going to do any real wilderness focus in your game, this is a great add-on. While not every campaign goes into the wilderness, there are even more city-applicable features like statistics for dogs, birds, and vermin swarms that would still be in play in a urban environment.
The Fair King Zoo scenario is both very interesting but also a little gory for my squeamish taste (it is a zombie game, after all). I'm not as easily scared as I used to be, so it didn't bother me terribly much, but it's not the sort of thing I'd run with just anyone (just like any zombie campaign). This should not be interpreted as a bad thing, however, given the setting and goal.
I cannot come up with anything bad about this book; some people may not care for the style, but I find the style to be incredibly cool (maybe on account of my nerdiness), and there's nothing I can gripe about.
My one warning to people would be that this is a zombie game, so not everyone will appreciate the art and content (it is rather gory), and it's not for children or the excessively squeamish.
For those wanting a quick summary:
Content: 4/5 (It has a lot, but it's very specific; if you are going into the wilderness specifically it'd be 5/5)
Art/Typesetting: 5/5 (It made my graphic design nerd happy inside)
Writing: 4/5 (Some typos detract from otherwise excellent writing, some places could be re-written)
Awesome Factor: 5/5 (ZOMBIES! Wilderness survival! Animals!)
Interest: 5/5 (Well thought out and deeper than just stating facts)
Maturity: 16+ (Clean language and sexual content, but violent and potentially disturbing)
Value: 4/5 (It's not the longest supplement around for $13, but it makes up for it with quality)