First thought: I like it. It's classic but simple. It calls out older versions of the costume without being too over the top. I even like how they gave her tights. (Why should she be cold?) But I also like it because, as readers of the Indestructibles know, Jane (AKA Solar) is a superhero in a skirt, and her teammates give her a bit of grief over it (particularly function-over-form specialist Kate/Dancer).
But Jane picked her own costume, and she chose the look not because it was feminine, or because she felt pretty in it, but because it harkened back to a now-gone generation of superheroes. Remembering the past is important to her, and her costume reflects that. In the Indestructibles, Jane, more than anyone else, wants to know and remember where she comes from and who came before her. History means a lot to her. And so she wears a superhero costume with a cape and a skirt, because it helps her remember people long gone, and because, like Supergirl, Jane is strong enough that she can compensate for some of the tactical impracticalities of a costume like that.
Like the Incredibles, we all know capes are an occupational hazard for superheroes. But if you're invulnerable, maybe it's okay to be a little ridiculous, if it helps you remember where you came from.
So there. I like it. I think it looks just fine. Because I like remembering where we all came from too. Even if Edna Mode says: NO CAPES!