As mentioned by another reviewer, this book is not about systems - it's about developing a vampire character and considering that development from a number of angles. How does aging effect your character? What are the effects of Discipline use on the character and those around her (and what Derangements are users of certain Disciplines predisposed to)? How does the loss of Humanity at various stages affect his outlook? These are the sorts of questions posed by, and answered in, The Blood.
The Properties of the Blood chapter basically goes through the special Vampire systems from the core book (ex. Predator's Taint, Frenzy, Diablerie, etc) one at a time and elaborates on them, adding a good element of flavor. For me, at least, these were often things I hadn't given much thought, but was happy to have kick-start for my own creativity.
The Vampire Psychology chapter is my favorite section of the book, giving suggestions for dealing with the effects of age and Discipline use on the vampire's mind. It goes dot-by-dot through the Disciplines presented in the core book, suggesting their impact on one's worldview.
Critiques? A friend and fellow storyteller doesn't think as highly of this book as I do, saying that there is little within that anyone couldn't have thought of themselves if they'd taken the time. He's probably correct, but as I said above, I appreciate the creative jump-start, and since reading it, I've incorporated it into the creation of many characters and feel it's had a positive impact on the depth of my vampire roleplaying. Another critique that comes to mind is a lack of systems; there's a table of modifiers here and an optional mechanic there, but not much in comparison to other books. That said, this book is really about Character from a narrative perspective, and performs well in that regard.
All told, this book easily among the three most important books of the line in my opinion (alongside the core and Damnation City). I highly recommend it.