The eyes seem to be different sizes and I think you're showing too much of his ear on the right side. I like the way you handled the wrinkles and the lips (something I have troubles with!).
I would also start darkening values to really make him pop out of the page.
 DRAW EVERYDAY >
The wrinkles are to strong, other than that and a few other things, yeah!
nice rendering, and with a few minor changes (some already mentioned) this is on the way to being a great piece. admittedly yes, his wrinkles resemble that of bedsheets at the moment, but it is a nice execution. i like your clean linework, this would work cool in any format (even vector reduced to a few colours.. hmm.. thatd be good ). watch that shadow on his chin, you dont need it to be your darkest value.
I don't see anything wrong with the sketch, all his facial features depicted in your drawing are perfectly believable to me.
Otherside is right about the darkness though, it will do the pic good if you increase the contrast a tad.