oh wow my post got deleted before posting... Retype:
the animations look quite fluent and on their own they seem fine, but here are some issues
Centre of gravity is off:
in the sideview, the arms seem proportionately shorter, and is exacerbated by an extremely low elbow joint. and as i said "on their own" the sideview in particular seems a bit mismatched perspective and proportionally compared to the downward and upward angles
also a quick edit pulling the legs back 2-3 pixels on each frame, and shaving 1 pixel from the height, however didn't adjust anything else:
ed: I also noticed on the contact of the right foot his leg grows 1 pixel longer. and his arms are changing length during their swing a bit too, this is kinda nitpicking it to a state of perfection, you could just assume most people won't notice, but I always think it's better to strive for something more solid and resilient to scrutiny. the shading is quite good, another thing I observed though is that in the upward walk his shading reinforces a far greater stride than the downward simply due to the darker shade of the leading leg going forward.
and on further analysis after staring at for long enough I believe your up/down ones have a bit of mixed perspective, the arms have significantly more foreshortening, as if from a more top down angle. and he legs look more straight on,
which when combined with the fact you might have pushed the tallness quite alot, makes them when possible to interpret a tad like this
edit: rushed example is too extremely exaggerated it could easily be interpreted as insult still extreme but more accurately conveying the effect I witnessed
and a quick colour of my first example just for funsake super funky hoola time
quite a strut, mainly the perspective issue and long legs vs shorter arms, this image is a rather extreme and exaggerated example but articulates my point sufficiently. perspective is a hard thing to nail, but you have a fluently animated base, the animation definitely reads quite fine, I just think you should work on matching the perspective of the arms and legs, It could be really subtle changes that will resolve it, could just be the long torso
one thing is that editing every single frame is gonna be a bit of a pain
okay staring even more I notice one more thing you're arms arc back and forth quite significantly and without any shoulder movement at all looks quite bizarre if paid attention too, and the extreme backward frame seems to convey a strange flick
and again just noticed something else that shadow implies his entire body is twisting, the shadow is being cast down from his entirety not just his legs, just something to consider, oh and also there is a brow region that flickers in the downward animation.
wow that was alot of critisism
hope you take it all as constructively as it was intended