I would try to drop the black outlines througout the image and lessen the banding.
pretty good job, but maybe contrast on skin could be slightly greater. Other than that, you have a lot of banding which is making your outlines a little blurry. I like the shading on the purple parts.
Ow, this is best of the best, and you is beautiful guy :3
These three DBZ portraits you've created are the nicest images in your gallery. They are fairly clean works of pixel-art that show off the iconic characters rather well. You did a good job translating your reference images to the smaller scale of pixel art. While I don't know if this type of work is appropriate for this gallery, I feel your description of this as Original Lineart is inappropriate; with a quick search on Google, I found the image you used as a reference in creating this work. The shading and lineart for this image all come from http://moe.animecharactersdatabase.com/uploads/370157020.jpg
I believe that re-sizing existing images can be a uselful excercise for learning pixel-art techniques. As others had mentioned, some of the lines show banding; the anti-aliasing could be improved in several areas. The outline around the preview image gives a similar impression. Reading more about anti-aliasing and banding would surely be helpful.