Whoa, HMC. Awesome stuff, especially the third portrait.
If you're open to some criticism, though, I'd suggest building the entire face in a consistent perspective rather than building the main features (eyes, mouth, nose) with their own vanishing points. To an extent, it's giving it some intrigue, but mostly it's making it look wierd. What I'm talking about is most evident in the chick's portrait, and I drew some lines in as visual aid for what I'm about to say.
http://i3.photobucket.com/albums/y73/SaboteurGreg/Portrait.jpgTake a look at the two long blue lines I drew. They're more or less paralell and you've used them (or imaginary versions of 'em) to create your cheeks and decide where the centres of your eyes and lips are. In terms of perspective, the paralell-ness works (I think?)... if everything else in the face follows the same paralells. That blue line under the nose shows how twisted that perspective is, which came about because you sent the eyes to a vanishing point that defied the perspective you'd set up, and then followed it with the nostrils, but when it came to the lips you reverted to your original perspective for the centreline, but sent the top and bottom of the lips to a vanishing point of their own, thus twisting the face further.
I think they're awesome anyhow. What you've done with lighting and colours (Especially on the chick, you nailed the colours there) is fantastic, I'd (and helm might, too) fuck a goat if you started constructing your faces with even more SCIENCE.
