Hello mate.The portrait looks flat for now.You have to learn working with hard edged brush(dont let it soft) and dont afraid to use the hard edged one.
You have to start studying values in greyscale before stepping into color.When you understand the values then color will be simpler for you and something more than simple apply of local colors here and there.
Do you have a sketchbook here on CA? if not start one and start your daily training to improve in everything .
I may be totally outside of your question by i didnt understand what exactly you mean by brush quality.I think the brush quality is good
(btw dont use only black for the shadows(shadows are colors,and black is not a color)because black makes the painting look muddy.
don't have sketchbook on CA yet... I'll try one of these days.. soon..
oh what I meant was brush strokes..hehe
yeah, I used black on the shadows.. I saw something was really wrong... now I know ^_^ thanks a lot for your advice.. really helps..
The second picture with the sun burst background kind of throws me off because the light source is directly behind her. If that is the case the shading would be the same on each side of her face and neck. keep up the good work.
I don't think brush settings are much of the problem, rather you need to do more studies to learn more about lighting and the planes of the body; this is where the real problem lies; not in your brush type. Try studying faces from life and checking out books such as Loomis and Bridgman. Keep working hard
The eyes should be given more brightness. Eyes should be real and the color of boundary can be made lighter. I wont think there may be problem with your brushes. The skin texture should be taken care of.