IDK, I've encountered several good stories where I couldn't sympathize with the villain either. Sometimes you don't want people sympathizing with the villain.
How would you feel if neither the antagonist nor the protagonist won or lost, neither was utterly destroyed and neither was in good shape at the end - however universe was saved and every other creature won?
Often a story benefits from the release of tension with a unsympathetic villain being defeated. I'm not suggesting all good stories should make you sympathise with the villain! But in real life, the villain tends to think they're the good guy.
I don't care whether the ending is sad or happy, what really pisses me off in both books and movies is when the ending is really vague. I hated the ending to Birds, for both the short story and the movie. Some movies, however, can achieve that vague-yet-interesting ending, such as Inception. My family thought I would hate it, but I actually really liked it. You were able to think up the ending by yourself.
I suppose the difference between Birds and Inception is that in Inception there are 2 very clear possibilities whereas in Birds you just don't know what happens next.
