A lot of it for me has to do with oppression of the people, concentration camps which from the time I was about 10 I was astounded by, and the fact that I know several survivors of that time, including some who were held IN the concentration camps.
From start to finish, the expense and seeing and learning what those people went through.
I tried, and still do, to understand the "logic" of Hitler himself. Wondering if he was simply just mentally ill, why someone would go to such great lengths to wipe out an entire peoples.
I also feel it is an important war for us to study, because so much of it is happening now, today. All over again! We even have people of power wanting concentration camps for gays. It scares me, and makes me wonder if it will happen again, which it very well could.