I have FCO and I'm not that big fan of it (but I know that many are). There's a lot of words in it, but not really many that are useful. Very thin on general plans and common structures &c in the openings, especially when it comes to 1.e4 openings. I actually think that the brief introductions in MCO are more useful.
Chess Opening Reference Books

A lot of the oldtimers still recommend MCO largely because of nostalgia for their youth when MCO was about the only reference around. With modern databases available I can think of no other reason that it is still recommended. Most people want explanations of the openings and MCO is pretty useless compared to almost any other opening reference. FCO seems to be the gold standard for 1 volume tomes precisely because van der Sterren will take a paragraph to explain a single move. Unfortunately, because you have already been exposed to more specialized opening books you probably won't be happy with any general reference work. They aren't designed to go deep or provide you with everything you need to add an opening to your repertoire. They're just designed to get you past the opening and into a playable middle game. I use FCO all the time when confronted with an opening I 'm not familiar with, but always supplement it with a database and usually a few dozen master games to get a feel for what's going on. Oh and videos and chessmentor lessons and youtube and even Wiki. So one vote for FCO, but I'm sure others will recommend their favorites.

And to complete my pro "why" over "what" rant from post #3, may I also heartily recommend Reuben Fine's The Ideas Behind The Chess Openings; 70 years old and still going strong (now available in algebraic).

And to complete my pro "why" over "what" rant from post #3, may I also heartily recommend Reuben Fine's The Ideas Behind The Chess Openings; 70 years old and still going strong (now available in algebraic).
I have that, but it was given to me, and I haven't looked at it yet. Thanks for mentioning.

In general the information you'll find in specialized opening texts will be much deeper and supplemented with more explanations than anything you'll find in a reference book such as NCO and co.
With the exception of FCO, which has the merit of explaining the basic ideas of many openings, the other reference books are not that useful these days compared to a good database with an opening tree.
The only advantage of an NCO or MCO is that by browsing through the main lines, you'd get some idea of the kind of position you could get out of an opening, but nothing you couldn't do more efficiently with a database in the first place.
Neither ECO, small-ECO, MCO or NCO are up-to-date, though it's not that much of a problem when playing U2200. I would have thought NCO was the most solid of the bunch (thanks to Mr. Nunn and co.) but I don't know about MCO, so maybe I'm wrong.

After reading Silman's article about openings (http://www.chess.com/article/view/how-to-learn-an-opening-and-more ), I ordered and received last week the FCO. It really is well-written.
It is now an active part of my opening library, which also includes ECO Vol.s A,B and D; SECO ; among at least ten other specific opening related books!
Still, sitting over the board after say 10 moves, I often find myself wondering what the real idea of this opening is, how to take advantage of my opponent's opening missteps, which piece to move next, what is the "book" move here or simply feel somewhat lost.
chrka wrote:
"I have FCO and I'm not that big fan of it (but I know that many are). There's a lot of words in it, but not really many that are useful. Very thin on general plans and common structures &c in the openings, especially when it comes to 1.e4 openings. I actually think that the brief introductions in MCO are more useful."
https://web.archive.org/web/20140626173432/http://www.chesscafe.com/text/hansen128.pdf
https://web.archive.org/web/20140626165820/http://www.chesscafe.com/text/hansen110.pdf

Still, sitting over the board after say 10 moves, I often find myself wondering what the real idea of this opening is, how to take advantage of my opponent's opening missteps, which piece to move next, what is the "book" move here or simply feel somewhat lost.
I understand that, for sure. I think that's why Dzindzi emphasizes the importance of having the sense of a tabiya and what kinds of (strategic) ideas are in it. The best of the "wordy" introductions to openings will talk about that. That's why I go with the "Starting Out" series. All of the ones I've been through discuss common ideas that shape plans. As you get better with openings, I've been told, you don't need those sorts of wordy books, because the concrete ideas in games tend to be very similar, and even the genuinely new ideas reveal the point of their novelty, if there is one, in analysis. Memorizing moves certainly isn't helpful, and that's why: you never know what to do next if you don't know the ideas.
One objective of mine, right now, is trying to figure out the/an appropriate approach to learning the openings.
And to complete my pro "why" over "what" rant from post #3, may I also heartily recommend Reuben Fine's The Ideas Behind The Chess Openings; 70 years old and still going strong (now available in algebraic).
https://web.archive.org/web/20140708112658/http://www.chesscafe.com/text/review315.pdf
hicetnunc wrote:
"In general the information you'll find in specialized opening texts will be much deeper and supplemented with more explanations than anything you'll find in a reference book such as NCO and ..."
http://www.theweekinchess.com/john-watson-reviews/nco-a-preliminary-look
http://www.theweekinchess.com/john-watson-reviews/more-nco-gambits-and-repertoires

A very good, if very old book for explaining the ideas and plans behind the openings is chess openings in theory and practice- Horowitz. It might help you with the why of opening theory.

I have ECO, an old edition of MCO, and lots of monographs. Some of the monographs are garbage, but many are quite useful. I never go through lines in MCO, but sometimes read the introductions. Then, I often go through lines in ECO, supplementing the study with recent games in Informant.
Horowitz, Chess Openings: Theory and Practice has better explanations than MCO in some cases. Recently, I was reading Fine, The Ideas Behind the Chess Openings and asking myself why I hadn't taken time to read the whole book. Of course, I was not agreeing with everything that he says. Some of his positional concepts have been refined and modified since he wrote.
I have found the Starting Out series useful.
http://chessskill.blogspot.com/2015/06/applied-study.html discusses how I go about opening study most of the time.

Oh I hope no one thought I was recommending Fine as your only reference book. We're big fans of "compare and contrast" as a means of learning.
... Neither ECO, small-ECO, MCO or NCO are up-to-date, though it's not that much of a problem when playing U2200. I would have thought NCO was the most solid of the bunch (thanks to Mr. Nunn and co.) but I don't know about MCO, so maybe I'm wrong.
https://web.archive.org/web/20140627022143/http://www.chesscafe.com/text/hansen116.pdf
https://web.archive.org/web/20140627063241/http://www.chesscafe.com/text/hansen145.pdf
A very good, if very old book for explaining the ideas and plans behind the openings is chess openings in theory and practice- Horowitz. It might help you with the why of opening theory.
USCF Sales is still selling it.

Advice: don't buy from chess cafe if you have another alternative, I did and they simply didn't delivery.

Because I love John Nunn's works, perhaps I should check out NCO... Have you ever looked at it?
Nope. I like Nunn, too, so I may get it. The problem with the kind of feedback I sometimes see from the forums is that it often justifies making all of the purchases I already wanted to make. Hmmmm...
I really don't know much at all about openings, and I know even less about opening reference books. However, I'm beginning preliminary study of openings, and I want to know what the values of various reference books is. For example, how helpful is the MCO, FCO, NCO, and any others you can think of. I believe that the MCO is the volume that is continually updated (inferior lines removed, new evaluations supplies, etc.), and contains mostly the just-business chess lines that are playable. Compared to the comprehensive ECO, I have been told it is more sensible to navigate the MCO, and that I should start there.
Any thoughts on which reference works are best to supplement whichever primary opening books I am studying? For context, I've done the "Starting Out" series for the Caro-Kann, the Ruy Lopez, the Dutch, and the Sicilian, and I am starting to go through "Mayhem in the Morra."