I really like the blue and gold armor... It looks pretty keen. Not so much the black an purple armor though, I think it's just because of the large purple parts on it... I don't really think that shade fits. That's just me though.
The basic idea of the helmet seems kind of bland, it looks alot like a motorcycle helmet (completely smooth) and not very futuristicy... It needs some cool details if only for aesthetics.
The shading on the helmet isn't that great. If you think about the shape of a helmet, the majority of it is really just part of a sphere... Maybe you should try shading the top/round part of the helmet like a half-sphere?... I know Tyrial had a pretty decent sphere shading tutorial around here... but the links are working anymore.
I'll post a sphere I shaded a while ago for a different example though... I'm not sure if it's perfect, but it's pretty close.
It's not much of a tutorial, but it's the best I have to offer at the moment.
Also, practice dithering alot for your graphics (Dithering is a sort of checkerboard pattern... like in my sphere). Dithering is an essential part of pixel graphics. Search google for some Dithering tutorials, Im sure you'll find something useful... Maybe you already knew about dithering... I just never noticed any in any of your work so I thought I would mention it.