Hi David,
In most of these I think you have controlled the light pretty well. Back lighting your subject always tends to give an ethereal feel to an image and also can help eliminate problem highlights and shadows due to the high contrast. If you do back light someone to control the Sun, adding some fill or even a frontal key light to balance the exposure and sculpt the face definitely helps pep up a portrait. With careful editing you can introduce this but, obviously if you can get it in camera, it saves you a lot of time in the long run.
I think the main problem with the photos is the backdrop. It's extremely busy and distracting and takes a lot of emphasis off the model. Generally I try to put emphasis on my subject matter unless the image requires and environmental shot - IE placing someone in their surroundings because it says something about them. Here I don't think the location particularly lends itself that well and so I would try and avoid distracting areas and create as much separation between the subject and backdrop as possible.