Have to agree with you, this is a beautiful portrait of the gorilla. Love the expression on his face, and the shadows around his eyes really make the shot. Very nicely done and thanks for sharing.
It's a good shot but can have more impact showing more facial detail and a tighter crop.
Try cropping about half of the tree trunk from the left border, and down from the top, almost to the top of head. Also cloning out the white vertical shape in front of it's face eliminates a distraction.
All very minor things, but the difference is significant.
I'm with Doug (Snapshooter), you've captured a wonderful facial expression but there is a lot of small things interfering with it's full photographic impact. A tighter crop and a little lightening of his face would make a big impact difference I think.