I think Rargh!'s questions are valid - everything mathers, everything is a part of the picture-expression. Im not trying to be hard, just pointing out that you should consider his questions.
Its very hard to give comments on the "pixel-skill", or atleast for me - since I think artskills are applied in pixeling anyhow.
You use the dithering - but whats intersting is why you use it and where.
I did a little hasty example:

This is ofcourse not pixel-skill per se, but a little form I think would be healty.
And if you want some more suggestions It wouldnt be pixel-skill neither, it would be the colors - I noticed the reds are pure red, and greys are pure gray - try to mix them a little.. My grays in this Is bluish in shadow and yellowish in light - same gues for the green character.
These things are ofcourse things thats not pixel-specific.
If this is not what you were after, Im sorry - its just suggestions and all my opinions - no offence was intended.