Bernd Eichinger is not a "respected director", he is actually not a director at all, but he is the most successful German producer of Hollywood style block buster movies (Das Boot, Neverending story, Name of the Rose, Werner, etc etc) - at least to the extent that such a film industry in Germany exists.
While it may be true that there was never a major feature film which focused on the historical Hitler, there is no lack of documentaries dealing with each and every aspect of his life one could think of, not only movies but also a lot of books. On one of those the current film is based on (Joachim Fest). So there is really not much cause for for controversy here.
In addition, there already was a quite successful art film that "broke the taboo" almost THIRTY years ago, Syberberg's
"Hitler, a Film From Germany" (it can be watched online). Bernd Eichinger happens to have been the producer of this film, too, BTW.
I think I will go and see this film. Not only because Eichinger's films are mostly okay, it features Corinna Harfouch. !!! .
I love her, she is great. And Bruno Ganz is probably Germany's best actor.