Very attractive 3 volumes; beautifully laid out and printed. Too much filler in the form of complete games and not enough instruction though IMHO. FCO has considerably more information. Nice coffee table books though...
Chess Opening Essentials: The Ideas and Plans Behind All Chess Openings

I agree with the filler comment about the games.
Regarding the instruction part, however... Is it that COE only seems to have less instruction compared to FCO when they present a given opening sequence, but since they subdivide the openings more than FCO (cover more lines, that is) that there may be more instructional content than thought? Then again, Gambit also uses larger pages and smaller print... I have only read excerpts from each, so I am also asking.

I may have been too harsh. I found volume 1 and there are a dozen or so little bookmarks strewn throughout so at one time I was actively involved with the set. I'm a big fan of being presented the same material in different ways to learn it, so for me buying the set was a no brainer. But FCO is like $30 so financially it made absolutely no sense especially since I already had and liked FCO. So maybe I was a little prejudiced from the start. It's all pretty much must know main line info though so I say go for it if you have some extra cash burning a hole in your pocket...

I have the entire 4-volume "Chess Openings Essentials" series. I also have "FCO Fundamental Chess Openings" by Paul van der Sterren. I agree essentially with baddogno's comments. The '...Essentials' series is good as an introductory survey-overview of the openings. FCO is also a survey-overview and very good for a single volume presentation. Looking though both of these, it appears to me that you will get about the same amount of information (theory) about the openings from both. But from an economics perspective, being a single volume, the better buy is 'FCO'.
Also it is reasonable to ask why someone would buy either books. The answer lies in the fact that they are both survey-overviews of the opening. If one intends to focus on a specific set of openings/defenses then (s)he will probably want to acquire books that are specific to the openings of interest. But if one is not interested or ready for such focus, but instead for whatever reason feels that a survey treatment, while not as in-depth, is sufficient their purposes, then the aforementioned books should suffice, again with FCO being the more economical purchase. Also, of course, the survey books make it possible to easily compare the various openings, and get a sense for what they are all about.

https://www.amazon.co.uk/dp/9056912038/?coliid=I1BYOXXYNIN94C&colid=2LP9S64U4UNM0&psc=0&ref_=lv_ov_lig_dp_it
https://www.amazon.co.uk/Chess-Opening-Essentials-Stefan-Djuric/dp/9056912690/ref=sr_1_1?s=books&ie=UTF8&qid=1529491739&sr=1-1&keywords=Chess+Opening+Essentials%2C+Volume+2
Etc.
Spongey – do you (or anyone else) have an opinion on this series of books as a possible one-stop-shop to the main openings? Thanks.
It is always the same problem with such kind of books. They are not suited to build up a repertoire, so how should we use it? Perhaps to get an overview on different openings before deciding for a specific repertoire. I would instead recommend a repertoire book from beginning on. The overview you can get from other sources like YouTube.

Good Chess Openings Books for Beginners and Beyond....
https://www.chess.com/blog/RussBell/good-chess-openings-books-for-beginners-and-beyond

Yesterday, I went to Barnes and Noble and had a look at the opening books. COE series is like an dictionary to me. I look up the moves and I learn that there is such an opening with some very basic ideas. I like FCO more because it focuses on the more popular choices, I think based on online chess database, rather than master database. I think I may be wrong about it but it is how I feel about the book. Starting out series is to learn the basics of an opening, not to build repertoire. Like, I quickly learn the standard moves, without trick or trap of an opening. So, I can play it and experience both win and loss. Move by move is the next step. After hundred of games, I build up my opening tree of a specific opening, then I read this series to understand the pros and cons of my move. I think this series have very limited amout of engine variationa. The advanced opening books are for repertoire, when you learn to win

Curious if it would make logical sense for someone to first read about ALL major openings in general (e.g. reading these opening surveys such as FCO, COE, or Watson's series) before they dive into specific openings to get an overview of the various ways to approach the opening?

It is actually not a bad idea to studying opening. Studying opening themes/ general plans and tactical ideas is necessary. Of course, it does no good to post-beginners like me to study long variation of an opening. But surely, I need to know what I must do in an opening.

OMG ...once AGAIN: OP is a 1300 in correspondence on here (LOL) and he's spending time studying the opening. You guys are literally insane and SO stubborn it's unbelievable. No matter how many times people tell you to stop worrying about the opening and to work on tactics/endgames, you're just DEAD SET on studying those opening lines that aren't helping you one bit, aren't you?
Hey, it's your dime and it's your time.
A lot of stronger players and coaches recommend a balanced approach to studying chess, which would include "openings", but for some of us, it is difficult to figure out how to "properly" study an opening appropriate for a lower club level without addressing which specific resources to use... then it comes across as "I am only going to study openings, 15 books in a row, tactics and endgames be darned."

OMG ...once AGAIN: OP is a 1300 in correspondence on here (LOL) and he's spending time studying the opening. You guys are literally insane and SO stubborn it's unbelievable. No matter how many times people tell you to stop worrying about the opening and to work on tactics/endgames, you're just DEAD SET on studying those opening lines that aren't helping you one bit, aren't you?
Hey, it's your dime and it's your time.
A lot of stronger players and coaches recommend a balanced approach to studying chess, which would include "openings", but for some of us, it is difficult to figure out how to "properly" study an opening appropriate for a lower club level without addressing which specific resources to use... then it comes across as "I am only going to study openings, 15 books in a row, tactics and endgames be darned."
Some comments recommended to study one specific opening for a week to know the standard lines as well as the ideas/pawn structure.... behind each opening. This includes replaying master games with the move guess. From that all, play that opening for a month and come back to the opening book for a week. And, repeat the same routine.
OP is a 1300 in correspondence on here (LOL)
Laughing at another player's rating is an enlightened thing to do. We all have to start somewhere, even you.
It is actually not a bad idea to studying opening. Studying opening themes/ general plans and tactical ideas is necessary. Of course, it does no good to post-beginners like me to study long variation of an opening. But surely, I need to know what I must do in an opening.
^ This. Despite our ratings, we still need to have some ideas of what we are supposed to be doing in the opening beyond very general principles, when faced with particular responses. And such an opening survey book will also help us create a very modest opening repertoire for use later on as we improve.

It is actually not a bad idea to studying opening. Studying opening themes/ general plans and tactical ideas is necessary. Of course, it does no good to post-beginners like me to study long variation of an opening. But surely, I need to know what I must do in an opening.
^ This. Despite our ratings, we still need to have some ideas of what we are supposed to be doing in the opening beyond very general principles, when faced with particular responses. And such an opening survey book will also help us create a very modest opening repertoire for use later on as we improve.
If that's how you learn best then I can't argue with this any further. Do understand though that simply using more advanced technology today you can basically read a book, listen to another one, and do tactics all at the same time. Not that you would do that but I'm sure you see my point. Right now, what good is the theory to you if you turn a +4 advantage into a -7 disadvantage in time trouble because you hung a piece?
Agreed on at least going over things to the extent that you're comfortable. As soon as I'm getting into more competitive games again I see that you're going to be surprised in the opening more. It's a one way ticket to time trouble and extensive calculation.
Your argument is just not sound to me. OP asks about the books he is interested in, not a way of learning chess or a study plan. Going off the topic is a good way to piss someone off, especially when he is serious about the question being asked. Just saying...

BTW, OP, I think the either the Starting Out series or the Chess Explained series are what you are looking for. Both of them explain the ideas/plans of both sides. Starting Out provides brief info and standard lines, whereas Chess Explained provides more in-depth details and longer variation. Move by Move series is more like an repertoire of one side. The book Four Knights Move by Move I am reading is for White only.

Good luck!
https://www.amazon.co.uk/dp/9056912038/?coliid=I1BYOXXYNIN94C&colid=2LP9S64U4UNM0&psc=0&ref_=lv_ov_lig_dp_it
https://www.amazon.co.uk/Chess-Opening-Essentials-Stefan-Djuric/dp/9056912690/ref=sr_1_1?s=books&ie=UTF8&qid=1529491739&sr=1-1&keywords=Chess+Opening+Essentials%2C+Volume+2
Etc.
Spongey – do you (or anyone else) have an opinion on this series of books as a possible one-stop-shop to the main openings? Thanks.