I have to admit I'm looking forward to this. I haven't seen or heard anything about this show that gives me pause. The only thing that even approaches a question is a lingering doubt that the production quality can be maintained (take a look at the first episode of House, for example, and you'll see production quality that is never attempted again).
Vox.com had a review today that makes me more excited for it than previously.
"There's a difference between a serious superhero and a superhero played seriously."
This sort of observation is like manna from heaven to me. It's why I didn't care for Man of Steel, and don't look forward to Batman v Superman. It's why I think Amazing Spider-man did less well than Raimi Spider-man. Serious superhero fits Batman in live action, and almost no other superhero.
It appears that Supergirl gets it. I can't wait to find out more.