This is the best introduction to wine appreciation that I've seen. Schuster begins with tasting (well, actually with glassware and looking), which defines the terms you see in most wine reviews (such as concentration, acidity, body, tannin, balance, finish, nose, etc.) and shows you how to apply them by suggesting a series of relatively inexpensive comparative tastings (including of non-wine items like lemon or sugar or coffee). There follows a grape-by-grape breakdown of white and red wine varieties, including a description of typical instances of the varietal for different geographical regions in terms you just learned. Included along with the wine profiles is a description of the wine-making process and variations, including champagne, fortified wines such as port, and even brandy.
This book is written for absolute beginners, but it's not an "easy read". The information is packed densely, and there are many invaluable practical "exercises". It reads more like an undergraduate intro textbook than like a breezy magazine article. Think of it as a wine equivalent of Julia Child's Mastering the Art of French Cooking, and you'll be in the right ballpark.
More than any other book, this one changed my perspecitve and took me from a struggling beginner level to where I can engage in wine discussions with experts. I found this book far more thorough than Hugh Johnson's pocket book, How to Enjoy Your Wine. If I was shopping for such a book now, I'd have to consider Jancis Robinson's "How to Taste", because she's one of my favorite wine writers; but I haven't read it.
After this book, I'd suggest getting Hugh Johnson and Jancis Robinson's World Atlas of Wine, and the Jancis Robinson edited Oxford Companion to Wine.