Well heres my 2 cents,
Instanly I can see that the stripes on the shirt are wrong and should match the place men of the shirt not the placement of the line
http://www.bridgat.com/files/LACOSTE_POLO_TSHIRTSWHOLESALE_SOLID_STRIPE_SHIRT_7.jpg like in the picture.
Not digging the black lines ither, I mean the outlines fine but it doesn't realy work as a dark shade. He also seems lifeless give him some more action.
Lucas's Shirt of Mother 3,Earthbound same game?
Any way I'd darken up the shades in the face, maybe give the face more structure, and then I'd remove some of the shades that a worth less, and are not noticible if missing.
IDK just something to thin about.
P.S all of those games are fine examples of great sprite work I realy enjoyed the use of color in Mother 3, so if you get the chance try looking them over.

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"Well, if you're still reading this, then stop. Go practice! Do a drawing. Just make shit, you know, something that is exclusively a product of you. "