Here's my review now that I've finished the book. First off, any fly casting book that mentions Dana Sturn and SpeyPages by name, along with Simon Gawesworth, has got to be a winner.
I've worked in computers for a long time. Computer books come in two types: big fat ones and little thin ones. The big fat ones have huge amounts of whitespace, repeat themselves over and over, and take forever to get to the point. They have extremely low information density. People buy these books because they figure that the fatter the book, the more it has in it. Everyone has a few of these book, but if given a choice, I'd rather not.
Thin computer books on the other hand are written by people who know what they are taking about. They are packed with information and usually need to be read several times in order to fully understand everything in them. They have high information density. I love these kinds of books. Which would you rather read? 150 pages packed with information or 1600 pages of fluff?
Jason Borger's "Nature of Fly Casting" fits into the information dense category. The book really should be called "Nature of Handling Fly Line". There is a lot more to this book than just casting. There is information on mending, line control, line types, why a reel is not just a line holder, what to do once you've hooked up to a fish, etc.
There are a few things I really liked about this book. Jason spends a lot of time explaining why a certain casting method, or mend, or line handling technique works the way it does. Many times a casting book will talk about a method with out saying why you should cast that way. Another thing I liked was the descriptions of fishing situations and the best cast and mend technique to use in each. Most books just describe a cast with no real context on how to use the cast.
Even though the illustrations are all line drawings, they are clear and get the idea across. It is quite difficult to use photographs to demonstrate fly casting. A still image of a dynamic process doesn't have the same impact that a series of line drawings does. A line drawing allows the reader to focus on the point being made by the author rather than the beautiful fishing location.
One of the things I'm not sure I like is the use of a modular description language to describe casts. I do agree that in many cases a casts can be broken down into smaller pieces and swapped with other pieces to make new casts, but the modules seemed contrived. On the other hand the modules do make it easier to remember the various casts and clarify the explanation.
All-in-all I really like the "Nature of Fly Casting". I think it will find a place in my permanent library.
Oh, yes, the book has a section on Spey casting. It is relatively short and simple, but is reasonably well done. Jason points to Simon's book and materials by Dec Hogan, Goran Anderson, etc. for more information on Spey Casting.