Actually I think there was a big improvement already when the swinging angles were halved:
Before:
After:
Maybe halve them again and see how it goes. Reducing the angle it needs to move will also make the movement slower without changing framerate. I think idle animations should be very faint. In minecraft you can barely notice them (btw, I think this one actually is looking already better than minecraft).
I actually like the "humping" so it makes it look like he's breathing.. but I do agree that it needs to me much more slight.
Also, maybe reduce the movement of the head more (or less) than what the thorax moves to get them slightly more detached. Try to use the head to compensate the movement of the thorax by making its effect less noticeable (making it less of a hump). This way it'll look a lot less like it has a stiff neck and maybe then you can reduce the lateral swings of the head.
For the walking animation, it would be much more realistic if the arms and legs could flex. Check out this animation:
https://www.youtube.com/watch?v=2aoa4Uo2S8gBut I guess that would require increasing the number of polygons so it won't be likely to be added to minetest_game...
We should have, imho, a version of the game for low specs hardware and another for modern hardware. Or allow texture packs to also change models and sprites (like replacing 2D torches with 3D meshes), then offer an official HD pack.