Although there is a lot about Machiavelli in this book, and there's some interesting advice on running a government tied back to the Florentine thinker, in fact this book is far more interesting as an insight into the workings of the Blair government.
To be fair to Powell, he points up a fair number of failures in Blair's decisions (and, by extension, his and the other members of the team). However, mostly this is an in depth hatchet-job on Gordon Brown and his followers. Now this might be well aimed and entirely fair - I don't really know enough about the subject to judge - there are certainly a number of anecdotes that, if true, make Brown sound not only flawed, but actually mentally ill.
Taken for what it is, an entirely biased (and admittedly so) insight into the Blair years it's a fascinating document. Little is made of what seems, at least now, to be the defining decision of the Blair years, however - following Bush into Iraq. It's not glossed over entirely, and Powell makes some sort of case as to why Blair made the decision that he did, but the arguments put forward are less than persuasive and if explored in detail actually amount to a pretty damning inditement of Blair's decision (although Powell clearly doesn't intend them that way). Indeed, when it comes to Iraq, perhaps Brown's indecisiveness and contentment in not being liked could well have saved a lot of blood and treasure.