This book really is excellent in every way. I'm an intermediate/advanced japanese student, although I mainly study on my own these days. Because of that, I needed something to teach me some of the little things that are difficult to find in a book, yet are a big part of the language, and this book does that. It has a HUGE list of Japanese idioms, set phrases, and similar grammatical tools that are absolutely integral to the Japanese language, and I often found myself going "Oh yah, that's the kind of thing I would say in English, but never thought to learn it in Japanese!"
Basically, if you want to take a break from the textbooks and learn some really good fundamental and natural Japanese grammar, this book is for you. For the price, you simply can't beat it. I also HIGHLY recommend "Basic Connections:Making Your Japanese Flow." With those two books, you'll have enough info to last you a long time!