Hey, this looks pretty good! There's a few little problems with proportions, and also the geo in places could be collapsed/ redirected... Nothing too bad
I was working on Low-Poly characters for awhile, about 8 months ago for a small Unreal Mod that died (sigh..) , but anyway.. during that time I collected a bunch of references form, wire frames images of models, to photo references, to orthos. So let me know if your interested, and I can zip some stuff up for ya, and send it your way!
Anyhow, nice work so far!
"Your weapons are no match for ours! People of Mars, surrender!"
"Um, this isn't Mars. This is Earth."
"Earth? Earth-with-nuclear-weapons Earth?"
[long pause] "Friend!!"