First thing first, Aniplex USA dub trailers are awful. Nothing to do with the dub voices themselves, but the trailer does a terrible job at showcasing them and make the lines come across as awkward. When you watch the show and hear the lines in context, they sound perfectly fine, so for the most part I'm reserving judgement for when I actually hear the dub when it comes out. The trailer is not a good representation of the final quality of the dub.
As for the voices, I think it's a solid cast.
I honestly thought Carrie Keranen would've made a good Ryuko, simply going off her Casca voice, but I can get behind her as Satsuki, and the girl voicing Ryuko sounds spot on. Same goes for Patrick Seitz as Gamagoori and Sarah Williams as Nonon. I think Christine Marie Cabanos is a good choice for Mako, although I didn't get to hear a lot of her, but I was actually hoping she'd play Nui, because that would've been hilarious and kinda creepy. I'm glad they're going with "Goku" Uniforms rather than... whatever the hell the other subs did. Some of the pronounciations are a bit weird. While they're technically not pronouncing the names wrong, it just sounds a bit odd in English, but I guess it's just something I'll get used to and probably works for the best in some cases, like when Ryuko shouts "Kamui Senketsu." I'm curious as to who will be cast as Ragyo and Nui, but I rather wait and see than speculate. I tend to have a lot of faith in Bang Zoom!
My only real gripe is the pricing, as usual with Aniplex USA.
Also, is it me, or are dubs coming out far quicker now than ever before. Kill la Kill just finished airing three months ago and already they have a dub and an US release.