It looks really good! However I did notice that theres some issues with "backwalk".
First, the hands are on backwards, or at least look like they are.
Second, i'm assuming that what you did was take "frontwalk" and change it up to look like the back, which is fine, but it looks like the wrong arm swings forward on the step. So the left arm swings forward while the left leg is stepping forward.
Finally, the lines that I assume are either there to help distinguish the arms from the torso, or to outline the chest make it look like torso is on backwards, so it looks like the upper half is walking towards you, and the legs are walking away from you.
I think some of these issues are also present in "backrun" but I haven't looked too closely at it yet since i may not use it for my project. Other than that, it looks great!