One thing I've noticed is that in real life, when people cry tears flow from the inside corner of their eyes whereas in drawings oftentimes artists draw tears flowing from the center.
Another thing that makes drawings look unrealistic is that the characters are often "too pretty" - no one in real life cries with eyes wide open and lips parted in a charming way- their faces get all scrunched up, their noses flare out, their eyes and mouths wrinkle.
But of course realism isn't the end all be all. Lots of things are just down to personal choice.