Very well done. There are some aliased lines that would benefit from anti-aliasing and some anti-aliased lines that seem to have some banding. The outline on the back of his neck would probably be better as the darker color you used to outline the top of his head. That said, the most important parts - his eyes and facial features - are all very well defined. It looks great!
I always pictured heavy weapons guy as looking a little bit more blissful(instead of angry), so this just looks like him in a really angry mood. Very nice!
amazingly enough, a few of the class defaults have no hats. :P and sadly heavy is one of them.
I don't really play team fortress much, but from what I understand... hats! Aren't you breaking some sort of sacred law here? 
