I have never been a big fan of hers, but I do think the early work is good, although if her children were fat and ugly, no one would know or care who Sally Mann is today. She benefitted from the controversy, similar to Sturges, of adolescent nudity in her images whether she planned it or not. I am not too comfortable with some of it, but I would take it over Sturges' work any day of the week. At some point though her children, which were the subject of her success, didn't want to be photographed any more and I think that it caused her to try radically different things. Her work changed from a sort of honesty to relying on artifice or superficiality born out by the process of collodion. The fact that she wants all of the defects in the plate, and even encourages the defects, seems to be a crutch that could be the result of her insecurity after her great success. The images that came after her family work haven't been greatly received, and the dead body images even resulted in having a show cancelled. If you see this in the documentary, it clearly shows her questioning what was happening. Her return to photographing her family, by photographing her husband, can be seen as an attempt to return the familiar, to what made her a success. She is concentrating too much on the morose if you ask me.
I have to disagree with Ian. I have seen many wonderful collodion images here and elsewhere as well. When the process doesn't interfere with the image, it can lend quite a stunning result that can't be duplicated easily, if at all, with film. I would remind Ian that the same could be said (although I am not saying it) for 8x10 platinum prints.