is this the four-frame walk? on the front-views it's obvious (and they look really good), but the sideviews don't have the right pendulum swing and might as well be rpgmaker three-frame walks. i know that i don't have to link you to references for a proper walk cycle, and you're too good to fall into that step-idle-step trap. it's obvious that you HAVE the right walk cycle, but it's not exaggerated enough to be noticeable.
the problem is that you need to pick the legs up more. i know it's hard with such a small sprite, but i think you could absolutely lift the feet off the ground by a couple of pixels for the passing frame.
and on the back view, work some more to put the highlight on the heel. remember that the foot is being dragged towards the camera, so focus on that aspect of the animation. the back-view animation is hard because you can't use knees and feet with as much definition as the front. look at what i did for my sandfall guys.
(hmm i think there's something off with the head placement in that gif) now the legs are a lot more exaggerated than yours (my sprites are slightly bigger and i can afford to do that because i have 8 frames), but the thing I want to show off is the way the feet grow as they get closer to the camera. it helps with the illusion that the player is sliding them across the ground (or, more accurately, that the feet are slaying in place but the character's body is moving forward).
your front-view animation does this really nicely but the backview is jerky and looks 3-framed.