What I really despise seeing in a story or setting is the monster treated as basically a human in an unusual shape or with unusual powers, but with human desires, human motives, human methods, and human modes of behavior. That I think is the real creeping problem in D&D and modern fantasy in general. It's not merely that the monster is treated as mundane because myth assumes that monsters are mundane, albiet just over the hill there along with other fantastic beasts like giraffes, hippopotomi, and panthers. The problem is that monsters are assumed to be merely human. This is a degree of familiarity and normality that far exceeds them being merely mundane. This is the real failure of imagination.