its frustraing to ask for replies and get none. i hate that. so heres one.i think its a good drawing. you captured the likeness well. its definitely him.
that said, i think there are a couple problems.
first, the contrast between the background and the subject is too abrupt. try to soften the edges a little. second, the entire head is slightly too long, which is not really fixable, but it is fudgeable. here are a couple things, realted to areas that dont include the features.
the turban is set too high on the forehead. this does too things. first, it makes the subject look odler (high hairline). second, it throws off the chin, which is about right in your drawing on its own, but made to look a bit astigmatic by the high and long forehead. finally, it makes the head look too thin.
ok, next thing, the collar is a bit low, making the entire thing seem too long.
lastly, there are some other contrasts which should be belnded and softened. the lines under the cheeks (esp on his right side), and the lines the come down from the nose to the corners of the mouth. and the drapery folds in the turban are not graduated enough. on the chin, you have the opposite problem, namely that the chin is not broken down into its various rounded surfaces. thus, it appears flat, too large and too long.
when trying to determine value, here are two tricks. first, squint. this eliminates detail and makes overall relationships easier to spot. second, use a constant value, like the round pad of your thumb, as a measuring tool. is this darker or lighter than my thumb> how much? once you get the main lights and darks in, you can use them as the barometer.
good luck, and it really is a very good lkeness.,
jai guru deva om