Hokay, let's see here......

1. The arm and shoulder are at dynamic opposites. Stand up and throw a punch, with the opposite hand on the shoulder, and you'll see what I mean. With the punching arm at full extension like that, the shoulder is depressed, as you have already expended the energy in the punch. But in your example, the shoulder is raised, as if the punch is still ongoing....which doesn't match how straight and low the arm and fist are. They -are- done with the punch. Drop the shoulder a bit, until it looks as if the entire body mass was behind the punch.

2. The upper one actually looks better to my eyes; in the lower one, his expression is more like 'Oh shit, I've been kicked in the danglies...!' The eyes are narrowed in anger. Lifting a corner of the mouth open more, so it looks more like a snarl, would help there. Opening the jaw a bit, so that it seems like he is either exhaling explosively or growling something would also enhance the emotion of the scene.

3. The biggest problems is that neither image is truly finished. One of the biggest dramatic tools you have to play with is lighting. Take the upper one; Poser default lights, right? Here's some ideas to play with: a) place a spot to one side, and adjust it just enough to throw a reddish light onto one side of the face, then one by one, turn off the infinite lights. b) Make the light more a dark reddish, to make it seem as if he is flushed with anger and adrenaline. c) Crank the specularity on the eyes all the way up, so that they glitter in anger. If the  present light doesn't make them visible enough, then place a spot 'beside' the camera on each side and focus each one on one eye.

4. Other options is adding dynamic elements to the scene. A door burst through. Set up a wall prop and tack a dynamic cloth object over the opening, and simulate a curtain burst through. Maybe curl the fist at the wrist more. Put a coat on him that his blown backwards by the wind of his motions.