Not much to say.
It looks promosing ,you just need to convert it to a more starfarer like sprite.
just one thing. the fron seems a bit flat.
is it flat or are the side surfaces sloping?
There is no rule saying it has to match game art
i am not saying it has to.
just comparing it to his other works and i would say he is making spirtes for a non-total conversion mod,
therefor a matching art style looks best in my and most people's opinion. (you dont place tf2 characters in a call of duty enviroment)
If he would tell me that he is planning on making a total conversion which i did not presume out of previous conversations and his past sprites,
I would emmediatly withdraw my comment.
Also no comment about any sprite is based on rules.
There are no rules for shading in art.
There are no rules for engine size in art.
There are no rules in art!
Comments about the sprites are based on personal opinions and accepted opinions.
if you are referring to the rules i made at the main page.
the accepted opinions dont have to contain something like imo (example: shading)
only the personal once (example: shapes, style)