Ledger was a gifted actor and his role in Brokeback Mountain was just one of the most moving things I've ever seen.
I don't get into celebrity worship culture, but I do feel a personal affinity for people who have done something I think of as a social good. Brokeback Mountain, and especially his part in it, was a major social good, as far as I'm concerned. It transformed the points of view of people across the country and put a human face to gay men that had been sorely lacking in mainstream movies, which often depicted gay men as either social eunichs or flamboyantly over the top. There's nothing wrong with either of those as part of the spectrum of the behavior of gay men overall, but as primary roles in mainstream movies, it's a bit thin.
Ledger, along with his director and costars, managed to bring human faces to the plight of those of us who live under the threat of violence for the nature of our very beings. For the loss of someone so willing to give of himself to play such a part, I'm going to miss his work dearly.