It looks like you've got placement of the shadows pretty much spot-on... try using a mostly opaque really big brush to smooth things out.

Is the lettering on his shirt mirror-writing?

Hmmm. Maybe add a few highlights? I noticed the black hair over the black facial markings kinda blend together and make it hard to determine depth of the face, so it looks a little more flat than the rest of the picture. Also, I think the left arm (the one over the guitar's body) looks a little long to me, compared to the right one. The upper arm looks a little more elongated than the other. That could just be me, though. (sorry if I'm being too critical)

It looks pretty good to me so far. I can't wait to see where you go with it.

the background looks like one of those sheets with designs or pictures that they have you stand in front of at sears when you have portraits taken :)

that isn't really a compliment or insult, just an observation