I think problem #1 is that you have a bunch of meaningless pixels scattered over the piece, making it look noisy. Zweck cleaned it up a bit, especially the coat. If you're going to place pixels, don't do it meaninglessly. The pixels must represent something.
Problem #2 is the stance and general form of the body. It's so round and indefinite, and the legs look very forward facing while the upper body is rotated.
Problem #3 is the palette. There is a little variation, but overall it is just a straight ramp for each color. Be bolder with your colors, and don't make a color closer and closer to another just because they look weird if they separate at all. This usually means there is a problem with the placement of the pixels.
Problem #4 is probably the black outlines. Don't get me wrong they can be used well, but often they just take up space and are a crutch when you can't get the volumes with shadows.
In my edit, I basically just started over, except for the head. Your head isn't bad, I just took it and modified it quite a bit. The body, I essentially took one color and drew the silhouette (minus the arms), then drew the coat and stuff over top of it. Then I added the arms. Color wise, I made his skin shadows go into green, and his highlights and lab coat go yellow. It kind of suggests an eerie light source, like a mad scientist or something. I enlargened the back of the head, got rid of the black outlines, and made the glasses and eyebrow pop off of it. There is definitely more I could do with it, AA and solve some of the banding issues, but you get the idea. Probably best viewed at 2X, that's the resolution I was looking at it.
Good luck.
Also, scientists are lifeless? I take offense to that, ha ha. But seriously, don't stereotype :>
