I used this book when I started learning Tibetan last year while living with the Tibetan refugees in Dharamsala, India. My (spoken Tibetan) teacher didn't agree entirely with Goldstein's suggested pronunciation rules and transliterations, but hey, that's no easy task no matter how you look at it - a fair number of sounds in Tibetan simply have no equivalent in English.
As other reviewers have noted, the gradations in difficulty are very well done. Things are explained thoroughly and in a logical order. Keep in mind though, this book (and language) is a serious challenge - not to be taken lightly. Goldstein throws a heck of a lot of information at you every time you turn the page, and when it comes to the reading passages he's not afraid to throw you in and see if you'll sink or swim! I think copying out, transliterating, translating and then trying to grasp the first lengthy reading passage (an old Tibetan folk story about encountering a goddess) took me about 3 hours of continuous work!
All in all, though, great. I still haven't finished the book (to do so would be a long project on solely your own motivation!) but considering how much I learned from getting through even a quarter of it, I suspect that if you slug through the whole thing you would have a pretty damn good grasp of literary Tibetan and be well on your way to reading the vast Tibetan literature. A rough glance at the vocabulary section suggested to me a total of 2000+ words are introduced throughout it all. If you actually acquired that much after going through the book and also grasped the grammar and so on that had been taught, I think you'd be sitting pretty!
Recommended especially if you are teaching yourself (as I mostly was).
[Addition in October 2010]: I finally finished this book a couple of months ago, as well as most of the other in-print textbooks of the Tibetan language, during a few intensive months doing little but studying the language. From my experience with the few Tibetan textbooks currently available on the market (I read through Preston, Tournadre, and Wilson), this one is far and above the best and most comprehensive. Goldstein's incredible thoroughness, painstaking attention to detail, and the very challenging nature of this book all come together to create an incredible experience. Unfortunately it is geared toward MODERN literary Tibetan and so it is not great if you want to learn Classical Tibetan, which is my aim, but you will learn an enormous amount from this book, perhaps more than from the other 4 listed above put together. Goldstein's philosophy is that reading actual, LONG passages is the best way to learn, and I would have to agree. It's also far more fun that memorizing vocabulary and grammatical rules! This is definitely the best textbook of Tibetan out there, in my opinion.