I agree with the other reviewer that this is by far the best introductory openings book. I also understand his point about Watson's uneven coverage in his otherwise impressive series, as I play the Petroff myself and can't understand its omission in Watson's book when there is a chapter devoted to the Philidor, for example. Back to the work at hand - it really is the best of these types of books (and I own Watson, Collins, Djuric series, NCO etc) and is a reprinted version of Sterrens 3 volume work originally published a few years back in Dutch, I believe. The quality of explanation is truly excellent, the depth of most variations' coverage is about right (although we will all have our pet openings that aren't covered as well as we'd hope for due to the inevitable space constraints - for example, I would like to have seen a little more on the Slav, especially the Chebanenko ...a6 variation) given the overall size of the project and the production values are typical Gambit, i.e. a step above Everyman but not necessarily in the same league as a typical Quality Chess title.
I have about 200 chess books and often find myself returning to openings compediums for a browse - this one has had a lot of use already and has rapidly become one of my favourites. For club players there is often enough to get up and running with an opening using this book alone - you can supplement it with the appropriate monographs once you've used it for a while and need more information, something that can rarely be said about NCO or MCO, for example.
An essential purchase, in my opinion.