Nicely captured expression, but I think this piece could be helped by creating some mood with lighting and eventually color. Decide where your light source is. Remember that lighting from below often creates a sinister look, which might be appropriate for this image. Imagine lots of contrast, chiarascuro even.
Also, the composition is a little boring. He’s stuck in the center without consideration to what will be in the background. Perhaps you could reduce him in size, offset him and create some element in the background that is causing this expression.
Just some ideas. It’s a good foundation.
M