The problem I see is that you're focusing on the motion of each individual part, the legs, arms, tail, head, and torso. But you're not thinking of the thing as a whole. So while all of those look pretty good, there is a bit of a problem when you see them all together. They don't seem to effect one another. He bobs up and down a little bit, but it doesn't feel like his weight is impacting the ground, his leg never bends to accept the weight of the rest of his body. His torso turns back and forth a little bit, but it doesn't seem to affect where the pivot point of the shoulder is. Another thing, usually when we run we are falling forward and then catching ourselves. So we lean forward. Your guy has a very vertical posture. Overall, I think you're very close to having something that looks really good. Just needs a little more holistic thought.
The approach that has paid off best for me, and the one I have seen used to the greatest effect, is to get a very rough shape animated as a whole. Then, go back and add the details and refinements to it after.