Sergio,
I am just blown away by the fearlessnes, originality and power of this portrait.
This reminds me somewhat of an Ivan Albright painting,
http://www.cegur.com/Albright/IvanAlbright.html though not quite so setting sun. They grab you and hold your attention from way across the room, everything else disappears.
I applaud your decision to refrain from sourires, as I think that is all to common in contemporary portraiture and diminishes the power of the painting. Try plastering a smile on an Ingres or a David eh!
I think your pastels could use a little more color variation and saturation.
I have been working in pastels exclusively for the last 3 years. I have an example of one in the introduction section. It is almost 7' high.
Your line drawing is exquisite.
Sincerely,