The best thing I can say about the Supergirl trailer is that it was better than the Jem and the Holograms trailer. Supergirl looks like it could be okay, but it's like the Saturday Night Live Black Widow parody... except meant to be serious. My issue with Supergirl is that it's as if the producers decided, "Oh, we have a female lead. Let's target a female audience. They like Devil Wears Prada and Gossip Girl, right? We'll make that but with super powers!" Well, no. Start with making a good product. Focus on what makes Supergirl a good character. That trailer is like a romantic comedy checklist with some superhero stuff thrown in. I'm a big Supergirl fan (obviously), and the sheer amount of cliches in that trailer is insulting. It's the lowest common denominator for a female superhero story.
On a more positive note, her costume looks a lot better in sunlight. I still would have preferred a unitard because the skirt just seems impractical for crime fighting.