Shooting the first three images in portrait orientation, would have helped a lot. Cropping a little bit off of someone's head isn't a bad thing. Cropping pretty much all of it is. 1 & 3 (in future, please number your images) look a little high on the red channel and are in desparate need of fill light and the background in 1 & 2 is rather distracting. The human eye is attracted to bright over dark; the background should never be brighter than the subject. The brick wall image is an interesting idea, and with a little less brick wall and a little more subject, and with her looking toward the camera, this could have worked well (don't forget to correct for perspective distortion). The last one, well... that's a taste thing, and I suppose it's not mine, but fair enough, it's a clever image. There are some over-bright highlights on her shoulders and forehead that need to be toned down.
Just my $00.02 worth - your mileage may vary.
~John