In the past year his reputation was shattered by revelations that parts of his works had been plagiarized, a charge also hurled against fellow historian Doris Kearns Goodwin.
In that he died from lung cancer, I wonder if he had been a heavy smoker.
Dr. Ambrose had the ability to write complicated history in a way that the average reader could understand and relate to the overall picture. He had much success as a professor and author and will be widely missed. May he rest in peace.
I wouldn't necessarily say his reputation was "destroyed", though he did have to deal with some truly adverse publicity over the attribution of a small part of his work as mentioned elsewhere on this thread.
I agree fully with your assessment of his work, however. His work with the national D-Day museum and on behalf of the written historical record regarding the American soldier in World War II are priceless gifts to history.