I think that the neutral expression would be fine, as even in the show that seems to be their default look. Like you said, until animations are figured out, we all just kinda gotta roll with what we got.
I changed the brow to be a bit more expressive/menacing, I might even do a few variants with different brows, mouths and eye direction. The biggest problem is that there is no random generation for static images as far as I know, so every possible combination has to be made manually and converted to dds with the appropriate settings, which will take a long time.
http://i.imgur.com/0pLLHFF.png