As I believe that the sincerity one brings to their life is reflected back through the legacy of their deeds, I can sum up my perception of Diana's legacy, at best, with a half full/half empty comment.
On the one hand, her work with AIDS and leprosy patients and, later, with land mines, represents the half full. Without any other context, without any other knowledge of her or her deeds, these acts must be respected, on their face, as providing a positive overall benefit.
On the other hand, what knowledge I do have of her personality and personal life (and considering the source of this "knowledge" is never first hand or personal and only as reported or, in a few cases, as she put forth) leads me to consider her legacy as half-empty. In some instances, I wonder whether or not any of her acts were selfless or whether they were part of a larger strategy of "domination" (for lack of a better word that won't lead to a treatise on personality and politics).
I think I had kept an open mind about her until I saw the Panorama interview. I remember flicking the television from live to record and walking away in disgust. I'm about the same age as Diana (born early 1962) would have been and was, therefore, around her age when I saw the interview. She was a woman putting on a performance and it sickened and revolted me and actually made me angry. She appeared to be trying to usurp the monarchy - or at least Charles - and I wondered at what point the poor woman began to believe her own press and took leave of her rational senses. She was, for all the world and on the world stage, a scorned woman getting hers back. Ugh. Whatever sympathy she might have garnered from me for her "lamb to the slaughter" rhetoric was slammed into rocks and covered with the sludge of what came next. I remember the predominant feeling was that I was sorry for her sons and deeply embarrassed for the Queen and the Prince of Wales.
What followed, with Dodi Al Fayad and the crash in Paris was, sadly, the stuff written on the subway walls, so to speak. Not that I believe anyone deserves death (or an inquest into their life after their death) but if it had not been a Paris tunnel, it would have been something else - she was a woman seemingly bent on self destruction. Her choice in lovers says a lot about her and her inability to understand her role - its limitations, its benefits and its provenance. The fact that she thought a divorce, while still the mother of the future king, would give her back privacy or take away her obligations to a certain level of behavior says more about her. It's a little like Garbo wanting to be left alone. Well. Greta, you ought not have made a spectacle of yourself in the first place.
The rest of us have to sleep in the beds we've made ... and Diana, Princess of Wales was no exception and, in fact, had a greater obligation to that metaphoric bed.
I think, overall, her legacy is a cautionary tale.