"... MCO-15 pretends to be everything for everybody, but it isn’t; it pretends to be up-to-date and relevant in all chapters, but it isn’t; it should be a good book, but it isn’t. ..."
And that was about a decade ago.
https://web.archive.org/web/20140626165820/http://www.chesscafe.com/text/hansen110.pdf
"... For new players, I cannot recommend books that use [an encyclopedic] type of presentation [of opening theory], because the explanatory prose that elaborates typical plans and ideas is usually absent, thus leaving the student without any clear idea why certain moves are played or even preferred over other apparently equivalent moves. ..." - FM Carsten Hansen (2010)
"... For beginning players, [Discovering Chess Openings by GN John Emms] will offer an opportunity to start out on the right foot and really get a feel for what is happening on the board. ..." - FM Carsten Hansen (2006)
https://web.archive.org/web/20140627114655/http://www.chesscafe.com/text/hansen91.pdf
Two other introductions to openings are Openings for Amateurs by Pete Tamburro (2014)
http://kenilworthian.blogspot.com/2014/05/review-of-pete-tamburros-openings-for.html
https://chessbookreviews.wordpress.com/tag/openings-for-amateurs/
https://www.mongoosepress.com/catalog/excerpts/openings_amateurs.pdf
and Winning Chess Openings by GM Yasser Seirawan (~1999).
https://web.archive.org/web/20140627132508/http://www.chesscafe.com/text/hansen173.pdf
"... Once you identify an opening you really like and wish to learn in more depth, then should you pick up a book on a particular opening or variation. Start with ones that explain the opening variations and are not just meant for advanced players. ..." - Dan Heisman (2001)
https://web.archive.org/web/20140626180930/http://www.chesscafe.com/text/heisman06.pdf
"... I feel that the main reasons to buy an opening book are to give a good overview of the opening, and to explain general plans and ideas. ..." - GM John Nunn (2006)
"... If the book contains illustrative games, it is worth playing these over first ..." - GM John Nunn (2006)
"... the average player only needs to know a limited amount about the openings he plays. Providing he understands the main aims of the opening, a few typical plans and a handful of basic variations, that is enough. ..." - FM Steve Giddins (2008)
"... For inexperienced players, I think the model that bases opening discussions on more or less complete games that are fully annotated, though with a main focus on the opening and early middlegame, is the ideal. ..." - FM Carsten Hansen (2010)
"... Everyman Chess has started a new series aimed at those who want to understand the basics of an opening, i.e., the not-yet-so-strong players. ... I imagine [there] will be a long series based on the premise of bringing the basic ideas of an opening to the reader through plenty of introductory text, game annotations, hints, plans and much more. ..." - FM Carsten Hansen (2002)
https://web.archive.org/web/20140627055734/http://www.chesscafe.com/text/hansen38.pdf
"The way I suggest you study this book is to play through the main games once, relatively quickly, and then start playing the variation in actual games. Playing an opening in real games is of vital importance - without this kind of live practice it is impossible to get a 'feel' for the kind of game it leads to. There is time enough later for involvement with the details, after playing your games it is good to look up the line." - GM Nigel Davies (2005)
Sitting in my Amazon cart right now are 'Modern Chess Openings; 15th ed.' by Nick De Firmian & 'Silman's Endgame Course'.
Can anyone purpose something they feel to be an invaluable chess book? Keep in mind I am only ~1000 elo. Thanks everyone!