Top-notch cast includes Joan Crawford, Fred MacMurray, Conrad Veidt and a good supporting cast. Plenty of charming Bavarian atmosphere/scenery to go along with the suspense.
I like the follow-the-clues aspect of the story, where you meet the various different characters in different locations as things progress.
This was Conrad Veidt's final film, as he died of a heart attack not long after production was completed.
A great companion film to this one is 1940's Escape, starring Norma Shearer and Robert Taylor, and with such greats as Mr. Veidt, Alla Nazimova, Felix Bressart, Albert Bassermann, etc. in the fine supporting cast. Highly recommended.
Yes, I've seen 1940's Escape a couple of times, and I also recommend it highly. Quite suspenseful. Sadly, Veidt was plagued with heart problems later in life, and finally succumbed. It was a tragic loss to the film industry and moviegoers.