A first for me!

[Judge_S]

I never make graphics. I started reading Spriteart.com though, and pixel art began to interest me.
Moving on to the basic ambient lighting tutorial, I decided to try to make a sphere. This is the result. Keep in mind, it's the first pixel graphic I've ever done, and graphics are definitely not my forté. I'm somewhat satisfied with how it turned out, but my eye isn't as trained to the faults in images.

Two images, one at 100%, the other at 300%.
Comments and critisism welcome, on such a basic image.