Stomach churning stories, either messed up worlds or worlds full of messed up people. Also, stories with disturbing hidden truths. You always feel the deeper answer lurking behind the corner but are never quite sure what it is...
If the anime was never completed, Then you're in luck. You can continue the story by reading the completed manga. This list has basically the same rules as a couple of my other ones, includes anime originally based on a manga, no...