40 years? How long do you think I took to finish Knuckles? Just a few months of dedication. :^]
Looking at the sprite, it is a really big improvement over the last KOTE. The anti aliasing needs some editing here and there, mostly on the eyes, the gloves, and around the stripes. My main problem with the sprite however, it's the choice of colors in his design. They are
everywhere. His shoes are green and yellow, his jacket has orange and gold, the gloves are red... He's not too far from being a walking rainbow. All the colors in his design are
unnecessary, it's just really weird looking at him. Making him have less colors in the sprite would be aesthetically better and make it more simple for the best of reasons.
On more so of the opinion side, though, KOTE's design was never interesting to me. I mean, he's almost like a Sonic and Knuckles hybrid, with a bit of Shadow in it. Personally, I never find it to be a good idea to work on fan characters all the way through like that, but if you really feel like doing it, I advise that you at least try making him completely different, starting by the face. Just looking at it already makes you think of Knuckles. You really should experiment with it and come up with different kinds of eyes and a different snout. Personally, I'd go with any other animal instead of an echidna. Hell, it doesn't even needs to be exactly Sonic styled to look good in game, because that could actually help differing him from Sonic and Knuckles.
If you insist on making an echidna though, my biggest advice is that you make it based on real echidnas.
Just look at it, a real echidna's head is a lot more rad.