Hey Costas!
I think you have a nice start! The over all highlights are fairly good, and mostly in the right places. I think from the nose tip and down it looks pretty good (nose looks nice too), but above this it needs some more work. The colors are fine, but more blaneding will be necessary, especially under the eyes. This will be easy to do though, just mix the color you used for the highlights and shadows and mix them together and apply thin washes until they blend together. The forehead looks pretty good, I would suggest to make the lines go all the way instead of abrubtly stopping (on his right side). I think the face could use a lighter highlight on the tips and on the top side of the creases.
The biggest thing to work on is the blending! Like I said, you have a great start, and the facial hair looks sharp. Keep it up my man!