I didn't like the previous version of Nitro's Knuckles, but this one is barely better.
I don't like the fact that the amount of reds the official Knuckles used had been reduced to only 3 in this character WAD. He also looks a bit too dark a red now. I think your Knuckles should have it's brightest shade of red made a bit brighter, and the other shades of red made darker, just so his sprites looks more like the official Knux's sprites.
I'm a bit happier about the walking frames now the head doesn't "wobble around", but his back walking frame still needs a bit of work, as I don't think Knux's head should turn that far left or right, should it?
Now the running frames still don't look that good, and the side running sprites don't help that much. Make his head a bit more forward and down, and make his dreadlocks move towards his back, so that he looks more like he's moving fast than he is now. The dreadlocks on the glide frames should have the same effect as well.
That's my constructive criticism for this character.