Old school art
This is a couple of years old, but Matt Finch’s comments in a Grognardia thread about old school art impressed me enough that I want to mention it here for my own future reference.
He says, essentially, that old school D&D art frequently depicts an environment and situation in which archetypal characters (often more roguish than clearly heroic characters) reach a moment of decision—a moment ripe with expectancy and sometimes wry humor.
This is not portraiture; you don’t see heroes posing for the camera. The art of David Trampier, such as the original 1978 cover of the first edition Players Handbook, exemplifies these criteria.