Wow, that's awesome... really well done man. You got the angle and shading perfectly. The only thing I have to say is that maybe his head shape could be more defined.
For example, have a look at this here image.
His head and face has a certain defined shape. His nose is fairly big/wide, and he's generally got fairly angry eyes. His eyes in the picture you drew are a little big, but that may be art style. And like Thunder Knight said, the facial hair is a little over the top.
Other than that, this picture is freaking awesome.
Buck now I gotta go play TF2 now. S'cuse me.