Red flags went up for me long before any costumes, plot or actors had even shown up on the scene, for one big reason. Even if all indications did look good (protip: they didn't), none of that would have changed the fact that David E. Kelley is wrong for this material.
Diana is at her best when she doesn't bother to hold back. Put her up against human criminals and the like and she just doesn't live up to her reputation (unless you do something really nasty, looking at you Max Lord.) Give her a god or demon or the like, and you see how she earned her spot on the Big Three.