The legs aren't going back far enough, which is making the walk look funny.
Have you animated a walk from the side? Even though it's not what you want, I recommend doing that for practice, so that you understand the motion that happens more clearly. It's much easier to mentally rotate your walker once you understand the motion as it looks from the side than it is to try to learn it in a more difficult perspective.
If you'd rather keep pushing on with this, I have one suggestion that could make things easier: Draw the character's footsteps on the ground, and animate the character following those footsteps, moving across the canvas for at least 2, preferably 3 or 4 steps. You can always centre the frames after you're done. This'll give you a guide to where each foot goes, so you'll just need to worry about connecting them.
In general, I recommend animating motion in motion instead of in place, as it's easier to spot mistakes that way, and things like sliding feet become less of an issue since you can see whether they're actually sliding, or just correctly pushing off the ground while the rest of the body moves.
