-Knuckles-

I think you did a nice job with the colouring and highlights. A bit chunky maybe, but it's a matter of personal style. There are some sharp edges, like particularly the one on his head, which would have been better as smooth curves. Using the jagged edges they draw in official art only really works if you directly imitate the Sonic Advance/Sonic Battle style. The eyes are likewise too pointed at the corners. You tried hard with the perspective on his feet, but they still look a bit twisted, sorry! I also think they eyes are just a little too wide for the head, and the iris and pupils a little too small. The pose is rather mundane, too.