I like the shading, it makes him look very spooky. Also, your detailing is pretty good.
I got to say, he looks more like Marilyn Manson than the Joker, but that's not a bad thing. That's just what I thought of when I saw this piece of art.
I've looked at your other pieces of art and think that you're a fine artist. I really enjoyed your piece of work titled "Hellmouth." Keep up the good work!