Hey dude I checked out your youtube channel, and even if you're not the best at animating with your movements right now, you have some really good effects and ideas, bound to be epic when you get better. Right now, your walk is stiff. Meaning the legs dont really bend that much like a normal persons' would. He's basically running with his legs stuck bent, and it looks pretty awkward. Try extending his back leg so it looks like he 'kicks off' more. The front leg also stays bent at the knee too which looks weird.
This was a walk I made a while ago. You can see how his legs are bent at certain times and straight at others giving it a more fluid feel to it. For a run you want to do the same, but extend them out more and adjust his back to the momentum.