I recognize Sonic, so you did well. I agree with what Kevin said about drawing attention with line weight, but you can also use it to give more of a 3D effect. Heaver lines on things closer to the viewer will tend to make them appear closer. So going heaviest on the right arm, a little less on the right side of the body and the least as you get to the left side will help make the right side seem closer to the viewer than the left side. Of course this can reduce the impact of his left arm pointing, so consider that as well. Kind of a balance between drawing attention and giving the appearance of distance.

I think you did a good job applying what you have learned. One feedback could be that I think you added too much line weight away from the focal point (which is the face), for example the shoes are too heavy compared to Sonic's head which is the most important part of the character. I can see that you added extra thickness on the shoes, index finger and quills which does add form to the character, but these lines are too thick compared to things like the head and the facial features. This results in the face being less noticeable, which is the opposite of what one would want from a cartoon character. I would keep things like this, but add extra weight to the head and the face, to make up for the stronger lines elsewhere. Anyways I think that you are learning, and that is the most important part!