Hey Matt, nice post! Quick question: are you thinking of adding a "bob" to the character's walk cycle? (i.e. on the frame when both feet are on the ground, the character is one pixel taller.) Even though this is a top-down game, I think it adds a lot to a walk animation.
That's a great idea! I'll definitely play with that tonight. In those frames from Day 2 if you look at Row 2 Columns 2/3 you can see the top of the head is more square which almost gives that same effect. Now that you mention the 'bob', I can see that's why that 'Up' animation seems so much better when I run it than the 'Down' (first row) animation.