Alpics Gorilla B/W won it for me. DoF and expression of the eyes both highlighted in comments. Guessing it maybe in a zoo which perhaps is why the look is one of sadness.
Wonderful animal, nice treatment...though I would have probably boosted contrast a little and looked at getting all of his chin in.
But as I say it is the eyes
Apologies for late post again.....somebody had me working on Sunday!