OD&D Volume I, Page 5, Annotated

Scope

Yes, "equipage" is a word. It is not a gygaxism.

The scope need not be restricted to the medieval ... This seemed a promise for various published settings for D&D that might stretch from the prehistoric to the imagined future. They did materialize, after a fashion, though TSR decided to go a different route. Rather than expansions or campaign-style releases à la Greyhawk, new games with their own unique mechanics were introduced (e.g. Boot Hill, Metamorphosis Alpha, Warriors of Mars).

Number of Players:

Much has been made of the from four to fifty players statement. Basically, campaigns could support a great many players but one should not assume there were fifty players to a single session. On any given night the number of players present would be similar to any modern day gaming meeting.

Also note: referee and other underlines for emphasis. When typing on a typewriter, machines in those days capable of italics were uncommon, so underlining was the standard alternative. Looking through the pages of these rules, one may perhaps wonder at the emphasis EGG chose to place.

Recommended Equipment:

Dungeons & Dragons (you have it!)  Why, we must ask ourselves, did Gygax feel compelled to point this out? Whimsy? Completeness? Stream-of-consciousness typing?

Dice: note the lack of usage of dice notation (d4, d6, d8, etc.); this terminology did not appear anywhere in OD&D or its supplements. Instead four-sided, eight-sided and the like were used, with dice being understood to be six-sided dice.

Preparation for the Campaign:

In spite of promises the rules will cover how to set up and actually play the campaign? This is one fo the few direct examples of actual advice on how to do it. D&D spread largely by gamers playing with an established group who then went out, bought their own rules, and began their own campaigns (though there were exceptions, including your esteemed editor).

This gave rise to a free-wheeling anything goes kind of campaign. Players had no guarantees about what they would see, their player-characters could do, or the exact nature of the setting until they sat down and played at a referee's table. There was no correct or incorrect way to play, and this aspect of gaming is one missed the most by players around during that time.

OD&D Introduction, Annotated

These rules are as complete as possible ... 

The introduction to OD&D provides an overview of the rules and structure of the booklets. From this opening paragraph readers are introduced to the idea of abandoning the mindset the rules are inviolate (your time and imagination are about the only limiting factors, or New details are added and old "laws" altered ...) but instead subject to the referee's whim.

And referee it was, the term dungeon master or DM appears nowhere in this work. As a historical side note: dungeon master and its abbreviation DM did appear in the first edition of that "other" game Tunnels & Trolls (on page 3 of that work, for example). Dungeon master doesn't appear in a TSR rule book until Supplement II: Blackmoor and there it appears as a compound word "dungeonmaster" (Foreword).

A good writer should always introduce important concepts and overarching themes first. Here in the introduction referees are advised to approach the rules as easily altered to suit their vision for their campaign. What are players told, one may well wonder? The second paragraph explains knowing the rules is an advantage and to keep a pencil handy for noting changes to the printed word. This implicit permission begins to shift with the publication of Advanced Dungeons & Dragons (AD&D) and the Dungeons Master's Guide which warns readers you must view any non-DM player possessing it as something less than worthy of honorable death (p. 8).

This quote, in turn, provides a glimpse into how the game and EGG's writing style began to change with time. Gygax began to write rules of increasing complexity and detail in response to what he saw as a demand from fans for same. After many decades, he finally returned to a simpler style of rules with both his Lejendary Adventures and using OD&D as his "go to" rules for running pickup games.

The final paragraph of the introduction maps out an overview of the three booklets. We start by learning how to make and equip a character, what monsters these characters will face and the treasures those monster are guarding. Last of all, we are introduced to the concepts of conducting combat, movement and exploration, and running adventures in a variety of settings (land, sea, air). As stated right up front: as complete as possible ...

OD&D Annotated

A closer look at a seminal work. 

Our purpose is drawing back the curtain of OD&D to get a glimpse at what lies behind.

Abbreviations used in this work include: 

OD&D: the first set of Dungeons & Dragons rules, OD&D being shorthand for Original Dungeons & Dragons. This the 1974 edition of the game that grew into whatever edition of D&D played at your home table.

EGG: Ernest Gary "Gary" Gygax, one of 2 co-authors.

DA: David "Dave" Arneson, one of 2 co-authors.

CM: Chainmail, a set of rules for miniatures warfare. CM included a fantasy supplement allowing gamers to recreate battles with goblins and dragons.

OS: Outdoor Survival, a set of rules by The Avalon Hill Game Company. The game involved being lost in a wilderness and attempting to both survive and escape. These rules formed the basis for outdoor movement in D&D.

FFC: First Fantasy Campaign by Dave Arneson and published by Judge's Guild. This work detailed the very first D&D fantasy campaign. Certainly other milieus existed in the imaginations of others before D&D gave structure to them. Other notable forerunners include Phil Barker's Tekumel, Forgotten Realms by Ed Greenwood, and Kalibruhn by Rob Kunz.

Basic History: 

David "Dave" Arneson (DA) formed the first fantasy campaign around Blackmoor, a small kingdom. Taking ideas from various games, such as ongoing campaigns around a location instead of a battle and heroes who would not die from a single successful attack, DA forged something entirely new.

Gary Gygax (EGG) eventually met DA and played in the latter's campaign and was hooked. The two men collaborated on a set of rules to be published and thus D&D was born.

Foreword 

Originally called the "forward" and corrected in the latest edition.

The foreword gives us some insight into EGG's thought processes as an editor and co-author. Gygax had long maintained the game was not based upon Tolkien's Lord of the Rings but rather on Burrough's Barsoom series, or Lieber's Fafhrd and the Gray Mouser. While this may be consistent with EGG's memory? The original printing contains references to Ents, Balrogs, Nazgûl, Hobbits, etc. These are  mostly expunged in later printings though a few escaped the editor's eraser.

Others present at TSR at the time said the inclusion of such was a sop to the many fans of Tolkien's works. While this would certainly explain their presence, many fans believe the reluctance of EGG to discuss the influence of the Lord of the Rings (LotR) on D&D may have had to do with the "cease and desist" letter received from representatives of the Tolkien estate.

In our personal conversations with EGG? His antipathy toward LotR seemed genuine. He claimed to enjoy Tolkien's "The Hobbit" but not the trilogy following that work.