For me it's two different one eldritch horror books or science fiction books where the enemy, this horror or alien race is suddenly understood and beaten by us humans, where instead of having this unknowable enemy or threat destroying our entire existence and we are barely hanging on, some child, dog or human with a macbook will come along and kick ass, oh and we have to have it from the bad guys point of view at some point so we lowly human readers can understand the angst in the heart of Cthulhu.
The second one for me is when you read the above book/series full of promise and build up and then the biggest enemies become other groups of humans, I know I get it humans suck but damn I wanted monsters and mayhem not another case of "shadowy organisation number 9945 hunting down the hero or heroine because she will mess up there deal with the old ones who will always betray them and kill them off in the last scene"
by Quebber