UPDATE:
Latest version, with dots for key points:
ORIGINAL:
I think his legs look pretty good, only his arms are really weird. people usually bend their elbows and stuff. Im pretty sure you can find tons of ref material for this animation online.
Thanks for the feedback. You're absolutely right - the arms are an issue. There isn't enough motion. I've taken it back to basics. I'm trying to get the forms down before I shade it again. Here's attempt 2, with more motion and bend in the arm:
I've reversed the direction so it conforms more with reference materials, which tend to face right. I've also decided to try and get one arm down before I work on the other.
It's hard to have perspective on my own work, but am I right in that his hand looks a bit too small or oddly shaped when it reaches forward? And maybe the thighs get too thick at the top on the forward step? Perhaps I could also change the hand in the down frame when it pulls fully back so it looks like it's flicking out just a tiny bit? I've experimented with that and it always looks unnatural, but there must be some way to make the arm / hand look less robotic or stilted when it's flinging out to the left. Also when it moves out to the front, in the two frames where it's most extended, I feel like the clean row of pixel on his forearm might be too noticeable. I'm not sure if that's an issue or not though.