a heelstrike is when the heel hits the ground. I always use that as the first frame when I make a run because I think it's that important.
It adds weight to the step. The character seems to not land his foot until the leg is straight below him. He should land the foot further ahead and plant the heel first on the ground.
If you look closely it looks like he's kicking in the air when he instead should be catching the ground falling forward.
I just did a quick edit but you could also trace each point and see how far the heels, the knees and the hands move in each frame. On the ground the feet should move at constant speed and in the air the heels should follow a teardrop shaped form going up in the beginning of the step (keeping the toes on the ground for as many frames as possible) and the go downwards while going forward all the way until the heel strikes ground.
I've never been a fan of too much head movements. For walks it's OK but when you run your head moves mostly from side to side like in your first post.
Having all this said, there's a million ways to draw a run and I like what you've got going now. The fully rendered version looks great; what a rock pose
