I think it's a good portrait, only a few things which I would like to comment upon, maybe it's useful to you.
The face on your work is lighter than in the photograph, which isn't a bad thing in itself, but because it is lighter, the difference in tonal values between the lighted part of the face and his white blouse disappears more or less. If the face is more in mid-tone with only a few highlighted parts (as in the source photograph), the tonal differences between face and clothing work better I think.
On the other hand, if you had made the face more mid-tone, maybe you would have needed another background, because then it would stand out less in relation to the background. (Choosing the right tonal values in the face/background and the white blouse becomes a bit of a juggling act sometimes.
)
I don't work in this medium myself. In some ways the transitions between certain areas in the face appear to be very coarse. Maybe it's a matter of style, maybe it's something to consider, whether it would be appropriate to make the transitions smoother. (Although, in this case it suits the character, I think.)
Peter