This is a very simple composition with a strong visual impact. The gorilla's body is on a vertical rule of thirds line while his head is on the top right intersection point. On top of that the eyes are on the top horizontal rule of thirds line and facing the direction of the empty space in the image. This combines with the crack in the background rock to give us a line of sight to follow, so we get a stronger feel of the direction the gorilla is gazing. The body posture is human enough to help us connect to the idea of a human emotion such as longing or meditation rather than the gorilla being "just an animal." The lighting is good as well with us seeing detail in the side of the gorilla and a nice highlight around the animal's face. The small bit of straw/grass on the gorilla's shoulder is a slight distraction but certainly not enough to ruin such a strong image.
You can read the story behind the image on the original submission page.