A couple of things can be taken into account when "rating" an avatar. Just the look, the degree in which it tells something about the owner (many of the avatars may have a meaning which no one but the owner understands), the question what kind of avatar it is (some create avatars themselves (somewhat more personal) from scratch while others use screenshots), etc.
I may consider the introducing effect of avatars a bit too important though.
Your avatar Mumbling is nicely done (+), done by yourself (+), but I don't think it can be understood without further explanation (-), does it introduce yourself? It looks a bit grimmer than I have come to know you
My rating would be 6/10.