If the light is coming from the top left why does the cast shadow fall to the left, towards the light? You say you have never taken anything to this level of finish before, if this is the case I recommend doing still lives with a single light. Study how light works and focus on removing the lines and instead using value to describe form.
Best of luck.
"The whole point of practice is to do it until you can do it right." - dpaint DA Sketch Book
hello Nuwan! i agree with element1988, study lighting and values as well! i would also add to study more face anatomy. Check this guy he's out, he's awesome! : https://www.behance.net/gallery/2146235/2011-B
as you can see, the underlying muscle structure of the face is still relevant to a certain degree despite the distortion and i believe that aspect of your drawing is missing. (the lack of cheekbones for example.