1st- needs a bit more color, maybe play around with color balance/hue.
2nd- add a bit more "energy" with the pen tool and it will be a perfect sprite.
3rd- i like colors and feel, but it looks like you just but render on background, and his hair is not very aesthetically pleasing, But i do love the color choices (peace/white)
4th- Too much negative/white/bright space in the bottom left, keep the glow around sword not illuminating out of it.