the light on his right, our left, eyelid is too light and it makes his eye pop out.
i like that you are very concerned about the modulations of the head, and with that i think you should pay more attention to the philtrum. since you gave attention to the philtrum turning up into his lip, particularly at that angle and with that side angle light, the philtrum would be more articulated. they're like two little pipes that roll out from the nostril, form a crevice between the two, and end up(as you have shown) turning up into the lip.
the turn of his cheek into the nostril is dark and distracting. it may be because of it's darkness or it may be because it should be turned with color instead of what looks like grey/black. because it is a gradually mild turn of form it should still retain it's local color.
the brow above the nose bridge should be centered....you have it more to his right.
nice attention to the rounded forms,,,chair, sleeve, etc etc. personally, i think the tree in the landscape is a bit distracting in it's shape. this portrait is a shape-dominant theme,,,you have big bold shapes. so the detail in the landscape looks out of place to me.