The new vertical motion feels more natural for this sort of stride. Personally though, I think I would've made the stride a little larger instead - the character lifts their knees a lot and it seems like a rather brisk walk, so the small stride isn't the most intuitive match for it.
I'm afraid I don't see the bending of the feet.

The elbow doesn't bend enough still, and the swing feels too fast when moving backwards. I think the problem is that you're animating the arm as forceful intentional motion rather than as a pendulum swing that slows down as it reaches the extremes and is at its fastest in the middle.
(Also, I think the arm might be a little too short?)

The legs move forward very quickly, perhaps slowing that down might help? Rather than move the existing frames though, consider adding some extra frames, to slow the walk down overall. That should help with the small strides not matching the fast movement speed. The backwards motion looks great already.

I'd say it's more that it's hard to tell what you actually want, OP. What is that tile meant to be? The title is "streetgrass" but is the tile a kerb, or a whole street, and where's the grass, where's the street? It might look good in context, but as just a tile, it doesn't read at all. What is the drawing meant to be? Even though it's "concept art", it's not doing a good job of conveying the concept, at least to people who don't already know what you're going for.
And what do you mean by "altering" the tile? Why not create new tiles according to what you need? Moreover, one tile does not make for an environment. Perhaps you should make (and show us) a bunch of outdoors tiles first, so you (and potential feedback-givers) have a sense of what your environments are like?

He doesn't look muscular at all, just due to the shape of the body - the arms are very thin and uniform in width, and the torso is very thin and flat, there's no sense that there's any muscle there. Consider drawing the body naked first, then put the clothes over it. The clothes will smooth over the details, but they won't reduce the size of the body.

I think that depends on the environment art. Out of context, it's hard to tell! I could see both of these being good.
One concern I have is that the shadows look rather grey. That's fine if your environments are largely grey/low-saturation, but if they're colourful, then having an ambient hue worked into the shading might look more lively and help unify the palettes more.

Pure black has its place in games, certainly. Many artists prefer to use a slightly lighter colour simply because such a colour can have some hue and saturation to it, which can contribute to the general atmosphere and colour scheme of a game, and because the less intense contrast can be easier on the eyes. If a saturation-less colour works well with your colour scheme and the contrast isn't an issue, then there's no harm in using black.

(Another reason to avoid pure black is technical - some systems treat pure black as transparent, or display transparency as pure black. To make sure the colour is visible and isn't ambiguous with transparency in any context, artists use a lighter colour for 'black", even if it's just a dark grey (e.g. 8,8,8).)