I like the zombie.
Some of your things look a bit messy, and the shadows on the first dude's jacket could use some lightening up.
For the zoombiiie...:
His feet are at a very awkward postition. The lowest pixels on both feet are on the same plane, so I'm thinkin' he's either being seen from straight side-on and is standing tippy-toed, or he's being seen from slightly top-down and his legs are crossed and very unbalanced. Either way, I suggest moving the far leg up a few pixels.
As for the animation, he looks kinda like he's dancing/humping something. I'm pretty sure that's not what you were going for. His legs and hips need tween frames. Right now it's just like he's jerking back and forth. Make it be like:
Starting at the left, accelerate towards the middle, then slow down as he reaches the apex of his forward thrust, then do the same in reverse. This way it'll look like he's got some weight to his movement. And believe you me, that massive back has got to weigh something.
The arms are jerky, too. You just need to smooth them out (which doesn't necessarily mean more frames!) Just do what I said with the legs (accelerate, slow down, reverse. Like a pendulum.) and it should make things look a bit more natural. In fact, just think of the arms as pendulums. They carry their momentum to their apex before it expends and then falls back down.
The orc dude looks cool from the shoulders up, but gollee, that saturated green is....saturated! But I'll just keep to the animation.
Like I said, cool from the shoulders up, but then down it's like...what is he doing? I can tell he's breathing (you pulled that off) but if this is an idle for a game or something similar where the dude's just supposed to be standing there...he looks like he's hyperventilating. Here's
a breathing idle I made. Might not be the best example but as you can see, breathing is usually pretty subtle. Now, on an SD sprite like this, you can exaggerate of course, but make sure he's not just having an asthma (or however you spell it) attack.
That's all I can type in the time I've got, so cya. I might add when I get home or make an edit.
