Technically, your exposures look correct. I like the single head shot best because the background is more muted (decent bokeh). Working with a model can be a challenge. Attention to details in posing, how the hair and clothing is arranged, what kind of makeup (or not, as case may be) is applied(and for what kind of light)--all matter.
Some of this can be adjusted or fixed in post-process. But in the last image the girl has a tired look and in a couple of the images I would have wanted her to bring her chin up or out a tiny bit to avoid an unflattering line.
Hopefully there will be better critiques coming. This is off the top of my head.