How could I have forgotten the Expedition to the Barrier Peaks?
I knew TSR dabbled with keyed illustrations in a three, early adventures. But apparently, the expanse of devoting so many pages to illustrations drove them to abandon them. As far as I know, only Return to the Tomb of Horrors, and the fourth edition, hardcover Tomb of Horrors continue the tradition.
In the third edition era, both Goodman Games and Kenzer & Company championed keyed illustrations. Kenzer even coined a marketing term for them. Almost all their adventures tout this feature: "ImageQUEST Adventure Illustrator: 'Because a picture is worth 1,000 words.' ImageQUEST is the picture book that gamers love. Now DMs can not only read the boxed text, they can actually show it to the players."
Just about all of the Dungeon Crawl Classics feature keyed illustrations.
Clearly, I'm not alone in loving them.
I seem to remember that at least one Dungeon magazine adventure made a bid to nostalgia with keyed illustrations. Can anyone confirm my recollection?