Definitely a good intro to traveling abroad. About 2/3 of the book is Travel Skills, but I think it's something that even experienced travelers could use; Steves provides lots of detail on things I wouldn't have thought to research.
When it comes to learning about the actual countries this book serves mainly as a good starting point. He devotes about 20 pages to each country that he chooses to cover (not all countries included) that gives you a bit of an idea of what you might want to see. After reading this book, I intend to research more on the places that got me interested, as well as research places he left out. (Milan, for example, wasn't covered at all.) Another iffy aspect of the Back Doors section is when he chooses to describe one experience from a city rather than anything else, such as when he describes watching geese get force fed in Dordogne to make foie gras-- not something that at all endeared me to that town.
This book is a great launchpad into other guidebooks and more specific research. But if you know where you're going in Europe, I might skip the Back Doors sections and pick up a more specific guidebook.