Visually it is a beautiful book that shows off Garr Reynolds design skills.
If you like discussing design and the art behind it, then this book is for you. It does a good job of discussing the design of presentations from an abstract approach, the writing style of his blog Presentation Zen shines through.
However if you want to improve your presentations this book offers very little. The useful information in the book could be condensed to about 20 pages; you may be better off searching the web for articles on basic design principles.
I picked it up hoping to improve my presentations, I walk away knowing about a few more free picture sites, having seen some great examples of slides and learn a few tips. Unfortunately the Zen of presentation design has not passed into my way thinking.