Cool. I quite like the sprite. The head has the problems mentioned already, but you show here that you obviously have the skill.
One thing I don't believe anyone's mentioned is that the hair (on the portrait) is over-AA'd to the point that it looks blurry instead of smooth. The palcement of the AA is fine, the grays just need to be darker,I think (and only slightly so). Also, the hair could use highlights, as they'll give it more depth.
The sprite, though... top notch. Nothing to crit, far as I can see. Nice stuff.
Keep working on that portrait. I'd suggest doing the lineart first, that way you know what/where to shade/highlight/colour generally. Good luck with it, either way.