You've shown a pretty good grasp of volume and proportion so far, but the shading needs to be even more extreme and the proportions more closely reflect the original reference.
- Shadowed areas should be even darker, using complementary colors instead of just more saturated hues. Then, to better define the volume, add a little bit of a rim highlight to the dark side.
- Give Scout more muscle definition besides in his arms.
- Scout's eyes are crooked, even if they're supposed to be almond-shaped in this picture.
- The face is, skull aside, rather box-shaped, and the potion of the face that the eyes, nose mouth are in should face distinctively forward, especially in 3/4ths view.
- The proportions of the face should be in rough thirds: hairline to brow, nose, bottom of the nose to chin. Scout's nose is, therefore, too low on his face.
- His chin also needs more definition. TF2 is a game full of Manry Men and Manry Jawlines of Masculinity, even on Scout. Generally, I also don't color lips on men since that gives the appearance of wearing makeup, but that's more of a personal preference.
- His cheekbones are, ironically enough, too well defined, making him look like he hasn't had a proper meal in ages. Smooth out some of that shading.
- His back and shoulders look a bit too high on his body, but that might vary from person to person. Consult pictures of shirtless dudes to get a better idea of how it's supposed to be proportioned.