Despite the thickness of the book, you won't find every illustration ever created for D&D. However, you will find a lot of illustrations, from as far back as the original edition (and before, in the case of some concept sketches) and artwork as recent as D&D 5th Edition. You'll find iconic images and rare concept art, images of vintage advertisements used back in the day to sell the products and posters used to announce product releases. There are also images of some of the pivotal creators and artists who helped to bring D&D to life, to the masses, and to keep it from going away.
One of my favorite features is a series of double truck (two-page) collections of images showing the various versions of a particular beast or character through the many editions. These are scattered throughout the book and focus on fan favorites, such as the Owlbear, Dragons and Mind Flayers, and even the fan-favorite character Drizzt. There are other, similar comparison layouts showing the evolution of the covers of some classic modules and all of the various versions of the "holy trinity" of D&D core rulebooks: the Player's Handbook, Dungeon Masters' Guide and Monster Manual, which every version of D&D from the original edition to the 5th Edition have had (although a couple of the names were slightly different in a couple of instances).
If you're a fan of D&D, be it old-school tabletop or computer games, pre- or post- Wizards of the Coast acquisition, newcomer or veteran player... or even a player only familiar with one of the D20-based products made possible by the Open Gaming License release, Art & Arcana will show you the influences behind your favorite version(s) of the game, the market forces that shaped D&D's development and growth, the things that worked well and the things that, well, didn't work so much.
Dungeons & Dragons: Art & Arcana A Visual History is a great coffee table book (and a great tome) for any D&D fan, perfect for flipping through for a few minutes while your party's wizard takes "one more minute" to finalize his spell selections for the upcoming day ...or to lose yourself in while you wait for the party's less-than-lucky rogue-loving player to roll another character. It would make a great gift for the D&D player who has everything... or just the D&D player who loves the game, but you're not sure what edition they play. But, if you're looking to get a really nice gift, you could also consider the deluxe edition: Dungeons & Dragons: Art and Arcana Special Edition, Boxed Book & Ephemera Set, which includes reproductions of classic D&D artwork that's ready for framing and a pamphlet-sized, previously unpublished original version of Tomb of Horrors, written by Gary Gygax, the creator of D&D, himself, along with some other artwork, all contained in a foil embossed clamshell case featuring artwork from D&D artist Hydro74. Looks like somebody's going to have a nice Christmas...