This collects ~74 pages of lessons that McGowan has published in Acoustic Guitar magazine. It covers the building blocks of "chord/melody"-style jazz guitar: "guide-tone" or "shell" chord voicings (just the 3rd and 7th, with or without the root), drop-two and drop-three voicings, close/block-chord voicings, walking bass lines, harmonizing melodies you play on the top strings, swinging the rhythm, chord substitutions/reharmonization, and an introduction to chord solos.
Compared to competing books that claim to teach you chord/melody style, this one stands out for being especially concise, disciplined, and methodical. Where other authors throw a bewildering grab-bag of tools and extended blather at you, McGowan is careful to convey the theory and purpose behind each trick he shares. Just skimming the book, you can clearly see where it's leading you, and can feel yourself progressing.
McGowan has superb talent, chops, and style as a "straight-ahead" (post-Bop) solo guitarist: Check out his online video of "I'm Old Fashioned" (http://www.youtube.com/watch?v=AXp_Wj3WSSw), or his CDs. But with a doctorate in performance, and a day job as a music professor, he also turns out to be an uncommonly effective instructor.
Oversize pages clearly show both standard notation and tablature for the musical examples. Those examples include whole-song arrangements that riff off jazz standards. The audio is pretty easy to download, as a single .zip file of .mp3's, from the magazine's Website.
Given the mag's folk-guitar focus, they've had McGowan create some unexpectedly sophisticated lessons in an extremely demanding jazz performance style. And given this book's origin as a series of separate lessons, it's unexpectedly cohesive. Strongly recommended.