Short (just 250 pages), sparsely cited, and drawn from a wide range of outdated texts and recent trade publications (only a handful of recent scholarly publications are cited, and the ongoing Papers of James Madison project is, shockingly, not among them), Brookhiser's book breaks no new ground. It skims the surface of Madison's life, but rarely penetrates into any particular aspect of the man's career or personality. His personal relationships are barely mentioned, while his professional relationships (with Washington, Hamilton, Jefferson, Monroe, et al.) are treated at only slightly greater depth.
Brookhiser's main point seems to be that we should see Madison as the father of modern politics, and he's correct to examine the man's role in the first party struggle of the 1790s (and to look closely and Madison's careful political strategizing throughout his career). But if you know anything about Madison at all, you'll probably come away from this book wanting more than you got. It felt to me like I was reading an abridged version of something that would have been better in a more complete original form.
The book was also marred for me by several errors, including, on the first page of the first chapter, the statement that Edmund Pendleton signed the Declaration of Independence; he did not. And the Federalist presidential candidate in 1804 and 1808 was Charles Cotesworth Pinckney, not Coatesworth.
Useful perhaps to whet a reader's appetite for Madison or as a very basic introduction to his political career. But if you're looking for the man, look elsewhere.