I haven't read the novel, so I don't know what liberties were taken to certain plot elements or characters, but from what I understand its pretty close.
As for the film itself it's fantastic. Herman runs a chocolate factory in the film. A great exposition into madness. Fantastic imagery expressing Herman's declining state as well the proliferation of Nazi propoganda, all melded together in this weird coctail. I love how color is used in this, very Sirkian. But then Sirk was someone he admired.