He has a happy crinkle eyed face, but somehow his eyes belie a bit of masked sadness just below the surface. Our faces become the roadmaps of the paths we've traveled in life. Some experiences etch more deeply into the terrain there--coloring and carving into new formations, like the wind and rain are wont to carve the soil beneath our feet.
The treatment in the upper left is a bit abstracted with touches of green and that happy turquoise. I'm finding the representation of "teeth" to be a challenge. A wise artist friend once told me to paint the light and shadow (cool/warm, dark/light), not necessarily the details of the object. Afterall, "it's just paint!"