In addition to Derrel's excellent points, I'll add that it's very difficult to pull off this sort of shot without some sort of fill light; even your camera's pop-up flash, if used properly (low output, diffused) would have helped dramatically.
Bear in mind that the human eye is naturally drawn to bright objects vice dark, in #s 3 & 4, the viewer is naturally drawn past the subject to the brighter sun and horizon. Generally speaking, the subject's face should be the brightest object in the image.
Also, avoid posing subjects, especially women, with their shoulders square to the camera ("football shoulders", #3).
Just my $00.02 worth - your mileage may vary.
~John