Nice start, I would check your motion curves, and turn on Trajectories if you have the option.
I don't know what program you are using, but in 3Ds.max, the biped skeleton has an option to enable Trajectories. It's like a trail that will show the motion of selected bones. You can see if the animation is wobbly or smooth with it.
Main thing to help the smoothness of the animation is the curve editor though. You have to go bone by bone and make sure there aren't any sudden changes in the shape of the curves, unless you really need it.
His right hand should stay more in line with the forearm.
His Left hand should be making more of a circle motion like his right hand, and in the same direction, clockwise.
His head, torso and hips need to move to show he is moving a large mass. Like a wave motion from the head to the pelvis. Head is fast, with the pelvis having a slight delay.
I wonder if the loin cloth and the little ones on his side have any bones to animate with?
I would add some animation to the cables also on his head.
His body seems a bit too thin compared to the reference. I know that's a pain to mess with after rigging, but can be done with morphing tools if you wanted.