I tend to find most of the catalog of D&D creatures and monsters to be a bit. . . underwhelming. Lovecraftian horrors, magical incarnations of every day creatures, mystical beings from other planes of existence and let us not forget the ubiquitous dragons. I suppose this is little more than the rejection of the standard tropes of fantasy probably best exemplified by D&D. There is just something about the existence of literal monsters such as the mindflayer that bugs me. Generally speaking, I think it is the simple fact that once you cast a monster as your villain, there is no reason to actually characterize them, to justify their actions, to understand their motives.
Of course, it must be said that my experience with the pen and paper game only extends as far as owning the manual - I've never actually played it myself. My only direct experience with the subject matter was in the form of games like Baldur's Gate and Neverwinter Nights. Neverwinter Nights 2 demonstrates this perfectly. While the game's chief antagonist is "The Shadow King", and there is at least a fair effort made to describe where he came from, it is only in the closing minutes of the game that he appears, as little more than the embodiment of malevolence, who's motivation runs entirely counter to his actions. Indeed, so deeply flawed is this ultimate terror that his entire purpose for existence is to preserve a kingdom he personally destroyed. The other antagonist, a human wizard of some renown, provides a better villain throughout simply because they were forced to actually explain how and why such a creature would ally with a monster known for destroying civilizations.
