I've read many reviews that sort of bashed the author and the story, which I admit had me going into this book with much hesitation. However, I decided to listen to myself and I read the book in several hours, for I enjoyed it.
The depravity of Hitler is all too apparent and I had to praise the author for describing him and his actions so well. More than once, I had a shiver go down my spine or I felt physically sick. Geli had my sympathy except in the moments where she almost seemed like she was truly enjoying the attentions of her uncle, who is shown as socially inadequate, irritable, abusive and demented. His awkwardness with women is mind-blowing and when you see how he treats them is disgraceful. Though he is quite settled in his anti-semite ways, he has not achieved his full transformation yet. This is in the late twenties and very early thirties, when the world was still getting to know him. His love for Geli is absolutely terrifying and all consuming, yet everyone envies the attention and gifts he lavishes on her. All she longs to do is live her life and perhaps get married before she's a spinster.
When it's revealed Hitler's molesting her, that is when his even more depraved side begins to show. By then, it's too late for Geli to escape his grasp and no one, even if they wanted to, could have saved her.
However, when she meets her death, which, though I'm certain you know she dies; I will not say how. You cannot help but feel terribly for her. It seemed as though everyone's back was turned on her, leaving her truly alone with only Hitler there--the one person whose attention she didn't want.
Even after her death, the loyalty to Hitler is undeniable and unchanging by most--including her own mother, despite the mysterious circumstances surrounding her death.