I think there needs to be a hem definition in the collar and the bottom of the shirt where it is usually hemmed down there.

As for the shading - try not to use soooo much dithering! I'm really guilty of laying on the dithers too much and then Demo usually reminds me to back off the dithers XD

But a dither should be there to blend the shades. If you can tell there is a dither there, however, there is too much.

This tutorial has a some good info on dithers: Pixel Joint Forum: The Pixel Art Tutorial

For shirt examples - try newer shirts (a lot of the older items on mene used a looot of dithers. But the newer stuff relies less on the dither. Wishie, the main pixelist, does not do a ton of dither and her stuff is gorgeous!) . My favorite one to look at is the pumpkin tee: http://www.menewsha.com/marketplace/...p?itemid=11185