Taking a violent, action filled movie and adding an unnecessary romantic subplot to appeal to the women.
Like Age of Ultron and The Hobbit. This is so unnecessary because women love superhero movies. If they are honestly worried about women not wanting to come to a superhero movie, they should know that since Chris Evans and Chris Hemsworth will starring in it will be more than enough. And if movie producers for the Black Widow add an unnecessary romantic subplot, I am going to scream. I won't care if I am in the theatre.
Not following the book.
This one is doubly bad because they didn't follow the book and it has an unnecessary subplot. They just took Legolas and said hey you remember him from the LOTR series, we are going to put him in every scene instead of focusing on the dwarves and give him stupid colored contacts.
Having villains that are misunderstood.
This is becoming so stereotypical and stupid. For this very reason, the live-action movie, Maleficent was ruined. Maleficent is mean and very sadistic and they ruined her character. If Hollywood producers ever think that having a misunderstood villain is a good idea, just look at Joker. People like Joker because he is not misunderstood. He is truly crazy.