Art is so subjective. It all boils down to personal taste. There are pieces of art I like better than the one I’m using as an answer for this question, but the question isn’t “What’s your favorite piece of RPG-related art?”
Two characters in a Dungeon, fighting a dragon. Dungeons & Dragons. Maybe it’s literal, but when I was a kid in 1982, I’d not seen anything like it. Something about Erol Otus’s art struck me at the time. It was at once grotesque and organic, yet seemed to hint of a world not like our own, a world of magic and monsters and heroes fighting against an encroaching darkness, maybe even finding treasure or mysteries that had lain undiscovered for ages.
I wonder whatever happened to that original painting and if there was more to it that what show up on the cover of that boxed set?