Without a doubt this is the best opening book to start with, and possibly the only one you might need for quite a while. Oh how I wish this had been available when I started out. What's the first thing a beginner does (ignoring all advice)? He starts surveying all the openings to find a few that he likes (and then changes his mind repeatedly). Before this book that involved buying a book on each opening, at great expense, both of money and time. That's no longer necessary - you can buy this one and get all you need for that purpose. It does expect some experience, but no more than any opening book does.
The book reminds me alot of Watson's Mastering the Chess Openings, except that it's much broader and less deep. It's far less selective and sophisticated than Watson, but it's not superficial at all given the target audience. It gives very good explanations of the general themes, historical development, and early move orders of pretty much every opening you could want, although it does have a strong focus on mainlines. For a beginner or intermediate, this book will give you enough theory to get started - your first half dozen moves with some deviations - but not enough to distract you from tactics and endgames. Coaches should love it. I'm sure they would tell you it's all you need until you are an expert.
The book is targeted at non-Masters. It's perfect for beginners to intermediates - I would say this is an essential book for beginner to Class C. Higher class players would still get a lot of value as a reference for unfamiliar openings they encounter and for broadening their repertoires, but I suspect an Expert would get diminished value from it. It has 450 some pages of large page size and has a huge amount of prose for each bit of analysis.
I bought this expecting to be disappointed by superficiality, but I was wrong. After the fact, it's hard to imagine this book hasn't existed until now. Thank you Grandmaster van der Sterren. Thank you Gambit.
Update: I find myself immersed in this thing all the time - it's addictive. I defy anybody in the target audience to read about their favorite opening and not learn something.