Here's what I would suggest as the very next step to improve the sideways walkcycle animation:
If you observe people walking, you'll see that there are two points in time where they have both of their legs on the floor at the same time:
- The right leg is in front, and the right heel touches the floor; the left leg is back, and the left toe touches the floor.
- The left leg is in front, and the left heel touches the floor; the right leg is back, and the right toe touches the floor.
In both cases, the head is over the middle.
Compare that to DBoyWheelers sheet posted
here: The third and fifth figures in the second row have a similar position, but the feet do NOT touch the floor at the same time, and the head is completely over the back leg. Let's turn the lower body a bit in figure 3 so that the feet line up and the head is over the middle (I don't have the source graphics, so I can only fake it here):
BEFORE

AFTER

Do this in the same way in figure 5 of the second row, too. This should improve the walkcycle a lot.
Yes, and listen too Mandle's tip, too: All the frames ought to have equal width, in each frame the feet should be right at the bottom, and in each frame the middle of the heads should be horizontally in the middle of the frame (it can bob up and down, but it shouldn't move to the left or right.)
Just my 2 pence,
fernewelten