I really liked them, but a few things:
1) Steele doesn't look anything like I imagined him to be, and I had a wide variety of things in that imagination. It's not his race/skin tone, but the fact that he looks...soft, young, too relaxed. He doesn't look anything like a Magnificent Bastard. In fact, I initially thought he was Admiral Bei (he looks exactly what I expected Admiral Bei to look like).
2) Sam looks a bit too Asian, given his accent (and that of his father and mother). It just doesn't fit; even if he was adopted, his accent (especially when put in the context of his parents' accents) just pushes the jarring factor too far, in my opinion.
3) Netreba seems too young and...soft?...to be a Fleet Admiral. I've never seen or heard of an officer of that high in rank looking anywhere near that young.
4) Byrne looks a bit too harsh, but that could just be his expression. Not only does he look like something straight out of a movie with insert-Commies-are-horrible-evil-monsters for villains. I think it's a combination of the wrinkles, facial hair, bang style (which is good, just not in this combination/context), and especially the cheeks/cheek bones. In all, it gives him a very pointy, jagged-yet-precise-and-orderly, sinister feel.
5) Where's Noemi?!
Simms looks great, as does Ng'Mei, Olefumi, Corey, and Calder (though I would personally give Calder a very thin layer of gray hair). Taylor looks great, though definitely not how I thought she might look like.