Great job! I love your colour pallette. It's very appealing. I may steal it for a future piece. 
I'm not usually a fan of perfect mirrored symmetry. It sometimes (usually) throws off the lighting and highlights of the art. With pixel art, the form is important and without a clear definition of where lighting is coming from it has a tendency to make a piece look quite artificial and maybe rushed a little. The eyes in this case give it away a little bit.
I like the line art style and I think you did great with Anti-Aliasing to break it up in just the right spots even if you only had to on one side.
Overall, super job! Keep up the great pixels! 
@DexRunner Thank you for the criticism!