Creating Capabilities is a significant achievement. Nussbaum has managed to accomplish four major tasks with her book, any of which would have made this a good book: write an accessible version of the Capabilities Approach; clearly differentiate her view from Amartya Sen's, who stands as the standard bearer of the approach; address some common criticisms of the Capabilities Approach that have arisen over the past decade; and to synthesize a large portion of her work over the past 15 or so years into a coherent whole.
The territory she covers is very familiar to those who know the Capabilities Approach. Capabilities are "substantive freedoms" - "a set of (usually interrelated) opportunities to choose and act" in one's life. They involve a choice between a set of activities for one's life, which are also known as functionings. So functionings are the active usage of one of your capabilities (e.g. voting (functioning) to participate effectively in political decisions (capability)). She also maintains the view that there are ten Central Capabilities, all of which must be grounded in a commonsense understanding of what a just society must have: human dignity.
One new feature of Nussbaum's approach is to split capabilities into two types: internal and combined. Internal capabilities are the general characteristics of a person (physical/mental/emotional) that are developed through interaction with external features of society. Combined capabilities are the "totality of opportunities [one] has for choice and action in [one's] specific political, social, and economic situation," which are the result of nurtured internal capabilities. As such, the two types of capabilities are interrelated, and cannot be separated within a society.
Another addition to the approach lays out specific principles which support the aim of a basic minimum or threshold of capabilities: Nussbaum utilizes the Stoic notion of the equal worth of all humans, as well as the Aristotelian notion of human vulnerability, the latter of which requires that governments provide citizens with the option to lead a dignified life via the freedom of choice. These two notions are crucial to her inclusion of the disabled, as well as efforts to include non-human animals in her sufficientarian theory of justice. Competing theories of justice struggle to include both of the aforementioned groups, since the simple fact that all sentient beings are vulnerable to some degree, which does include animals as well, means that no theory can capture what the average human or most humans require to have sufficient capabilities.
As far as Nussbaum's specific version of the approach goes, it's clear that she was making a clear break between her capabilities view and Sen's. Her view provides a means for determining whether a society's conditions are unjust. She contrasts this with Sen's view, which gives us an evaluative framework concerning quality-of-life, but does not seek to fully adjudicate what is just. In this sense, Sen's view has more in common with contemporary welfarist views on justice, and less in common with the development of the Capabilities Approach over the last decade.
If there's one problem I do have with the book, it's that I don't know that her version of the Capabilities Approach will convince many egalitarians to adopt it. For all the objections Nussbaum does try to address, it's not clear how she would address inequalities in society after the threshold of Central Capabilities has been met. That is, is an injustice committed if some citizens, say, live significantly longer than others, or are able to move freely with less of a threat of violence than others, simply because the affluent can afford to do so? So long as all other citizens live a normal life, and face a sufficiently small threat to move freely, Nussbaum seems committed to saying that this is acceptable.
But one might argue that simply having the income to purchase such benefits doesn't demonstrate that the inequalities between the two sets of citizens are just. For specific goods like one's respect within the community, a citizen's basic education, or health, it isn't clear why the Capabilities Approach should allow any segment of citizens to face significantly more vulnerability or a set of drastically reduced capabilities, simply because of wealth. She could counter by saying she has only set out conditions for what is minimally just, but this wouldn't address why some injustices should be allowed, and some (below the threshold) wouldn't be.
All in all, I'd recommend this book for anyone interested in a theory of justice that is accessible and innovative, particularly one that sets a threshold for a just society that isn't based on finding the right distribution of wealth or opportunities. I'd also recommend it for anyone unfamiliar with the Capabilities Approach who's curious, or anyone who needs a refresher.