not bad, i think the shirt is done rather well. i think you're on the right track with his face, looks kinda flat though (like a cell shaded cartoon). try adding more depth by introducing more extreme highlights and shadows perhaps? honestly, i do not like the background... a solid mid tone or a basic gradient may be better. keep up the good work!
You're focusing too much on detail. You're also drawing symbolic color, e.g. the eyes and shirt are "white" so you paint them with white paint. This is similar to painting leaves as being purely green, even though depending on the lighting they can be any number of colors. I guarantee you that if you use the eyedropper tool on the original image the eyes will be a much darker gray than they appear. Read up on some color theory. Also, work on the big shapes, not the small noodley details. Figure out what is in the light and what is in the shadow immediately, as your lightest dark should not ever be lighter than your darkest light (and the converse also follows). These shadow shapes are what defines our view of an object, not the details. Look at this to see a good example of how much information is packed into the shapes of the shadows. I'd also recommend painting exclusively in black and white for a while until you get good at judging value.