Note that not all monsters are created equal for metaphysical problems. You can have werewolves without asking as many metaphysical questions as for vampires and fairies, because werewolves aren't -- either in folklore or Hollywood legend -- vulnerable to holy things. And you can have vampires and fairies, with or without vulnerability to holy things, without asking as many as for angels and demons, because angels and demons have their every act connected to metaphysics. (If they are living lives like every other creatures, that in itself has implications.)
Some of the issues I have with them may be that so many of them use Hollywood lore. There was a situation where consistency was less important than in even most folklore. Not that it's ever easy, being convincing when smashing together wildly disparate tales.