Perspective and Proportion
An interesting portrait.
The way you have drawn him - the proportions with the head, how you have done the nose, and the way the eyes are - put me in mind of what you would get in you were looking at someone taller then you and they had tilted their head back a little to 'look down their nose at you'. Though, with that pose, the chin point would not be so prominent, it would look more flat instead.
They symmetry is off, but that is tricky to get right anyway and comes with practice. For a regular, face on view portrait, the changes in proportion I would advise are this:
1. The proportions for a human head is (to my limited art knowledge for humans) basically a circle with the jaw attached to the bottom. This is a circle with just the chin attached. Close.
2. For eye spacing, you need the space for a third eye in the middle (you have this here), but only space for about half an eye either side. Not including hair fluff, you have space for a full eye either side. Take that space in more and it would look much more in proportion. Also, aim to have the eyes just a fraction above half way down the head. Having them up a little like this is as you would do in a 'head tilted back' portrait.
And 3. Eye shape. For the average eye, the inner corner of the eye is low with the lower lid dipping down a fraction as it follows the curve of the eyeball out, but that is it. Most of the eye rests above the line of that inner corner. So more up curve then down.
The neck has been mentioned before by people and I agree it is a little long, though adding more jaw mass, as I said above, would take a fair amount of that away. The longer neck also adds to the 'head tilted back' look too, as more would be on show with that, though not quite this much I think. The thickness however is very close, just less then the width of the head as it should be - though you don't need to curve it out to match the lines at the side of the head, it doesn't do that so prominently and the jaw usually hides it in a strait portrait.
I like the hair. The light and dark differences make it look like it is ether catching the light or has highlights added, or both. The texture is good too.
All in all an interesting portrait with your perspective play. I have an enjoyed studding it.