General impressions before I get to more specific things later on:
I thought it delivered on the promise of the trailer, thankfully minus the cheesy pop music. Very Flash-esque in its structure and a little crammed as many pilots are, but the heroic moments truly shine, in part thanks to an incredible soundtrack and great CG, especially the plane sequence (although some later flying CG is pretty shonky and has that "obvious blue screen" feel about it - but this may be improved for the premiere). Benoist is really, really likeable - ambitious, bubbly, assertive in some situations but a total dork in others, thrilled at the idea of using her superpowers, but also doubtful at the possibility of her future as Supergirl. Arrow and Flash fans will find themselves right at home with this addition to the DCTV universe (but still begging for crossovers).