Hi Judson -
You've got a nice likeness started here... and it's so nice to have the reference photo to compare!
Some quick observations: The whites of the eyes and the teeth, and even the collar, could use some shading as they curve. I'm seeing more shading in his lips as they curve and a shadow that comes up from his chin to meet the shadow at the corner of his mouth. Also, when I squint at the photo, his hair is a much darker gray, fairly close in value to the lighter areas on his flesh. The hairline edge needs to be softened where it meets the skin of the face. I think the ear should rest a bit closer to his head than you show it (check the shape under it), and the shadows from the side of the cheek melt up onto that little flap at the front of the ear in the reference... but stop abruptly on the painting. Also, the shadow along (our) left of his face continues to be darker, as it goes up along the forehead. You may want to recheck the shape of his chin and jowls, in particular, you're showing the jowl on our right as much more square than in the reference. The irises of his eyes are just a tad larger in the reference, giving him a warm aspect, whereas in the painting he looks almost alarmed. You're showing some sharp highlights on his face that aren't in the reference - especially the vertical stroke between his eyebrows... There's more of a soft C there on his forehead with a crease from the browline cutting into it a bit. I'd lose the shadow on the wall behind him, and you might want to consider warming that color up a bit.
Hope I haven't overwhelmed you! I just know how much I appreciate 'fresh eyes' looking at a painting that I'm working on!