Review after reading part one:
Solid book, really does what it says on the cover: understanding rhythmic notation.
The book goes straight to the point. It starts by teaching simple notes and goes on adding other elements of notation, like bars, repetitions, rests, ties.... As each element is taught and complexity goes up, there are exercises to let it sink in.
I had learned this notation a long time ago and forgot all about it. This book is giving me a very good refresher. But what I like most is that it makes me pay more attention to the rhythm in my guitar playing. A funny thing I did is taking a strumming pattern I have played for a while and writing that down. It really makes you "think" about what you had been "feeling". By knowing and understanding the rhythmic notation of a pattern it also makes it easier to see what variations you can do on that pattern.
Comparing with other music books: don't expect this book to be a broader introduction to rhythm in music. It is not the rhythm equivalent of "Practical Music Theory"; this one goes straight for the notation and does it well. This narrower scope was not a problem to me, probably because rhythm is a much more intuitive and natural notion than all the "esoteric" theory behind harmony and scales.
Now, what past reviewers have said is certainly true: the text in the book needs some serious proof reading. There are frequent typos and mangled phrase structures. This is NOT a serious drawback because the text is still clear enough. The book's strong points are still very strong, but these things could be fixed if you are considering a print pressing.
Justin(s), from past comments you seem to be interested to know what these small mistakes are, so here goes. I have only read part 1 of the book. Also, I am not a native English speaker so most likely I also have errors in my corrections

Page 5, paragraph 4: "learning to these basic skills" -> "learning these basic skills"
Page 5, par 9: "therefor" -> "therefore"
Page 11, par 1: "the certain" -> "certain"
Page 11, par 2: "is becomes" -> "becomes"
Page 12, par 1: hyphen -> long dash. Happens in other places
Page 12, par 7: "divided" -> "is divided", or "divides"
Page 15, par 4: double space
Page 17, last line: second 2 should be 3. This is the only error in the "notation" I found.
Page 50, par 3: "better of" -> "better off"
Page 50, par 4: "with out" -> "without"
Page 72, par 1: "go pack to page" and then there is no page number.
Page 79, par 1: "we get we we use rests" ->

Page 85, par 3: "Sound" -> "Sounds"? Not sure what is meant.
Page 88, par 1: "then" -> "them"
Cheers