A couple of things I see right off the bat are there are a ton of colors here (I think 256) and the image looks as though you resized it, or at least parts of it. Did you make this bigger
to show people the detail? If so, the forum has a nice zoom feature built in already. If not, there are still some strange choices to me. Apart from the high number of colors, there are a lot of places where the linework is 2 or 3 pixels thick with no apparent rhyme or reason. Which again, leads me to think you blew this up for us. However, if you were wanting it this size not just for us to see, then you should go back and clean up a lot of your lines. In my opinion, it is fine to enlarge something that is originally yours, but you still have to go back and clean it up.
Also, his arm looks very strange to me. I can see you are going for some muscle definition here, but there is so much going on that it looks very jumbled. The arm is shaded strangely as well, which is not helping. It appears as though the light is coming from the upper left, but the way that his right arm is shaded is almost as though the light is shining directly at it. It almost looks pillowy. A little more contrast may help that.
A-ha! I found your other post with the sprite (thought it looked familiar) and am using that to show what I mean. Also, I see that the sprite itself is 60-ish colors, which is quite a lot. ndchrisite already gave you some good crits on the character in your other thread (including the arm).
This is just a pretty quick edit where I changed the arm some and got the colors down to 41, and you could probably get it even lower fairly easily.
You may even be better off simplifying the arm some with that more toonish look that is going on. All up to you though.