I can't think of a single bad performance by Conrad Veidt in any movie I've seen him in. That doesn't mean he was not in some poor movies, of course. It means he was always believable and interesting, whether playing Death, Jesus Christ or the Nazi-est of Nazis.
One of the poor movies he was in was KING OF THE DAMNED, one of British Gaumont's attempts to break into the American market in a big way with an expensive production and American stars -- here Noah Beery and Helen Vinson.
Veidt, Beery and an assortment of actors are prisoners on some sort of international Devil's Island, where Helen Vinson is visiting because her father is commandant. He's dying, and his replacement is so bad, the convicts stage an uprising and win. Of course, Veidt and Vinson fall into Production-Code-limited love, and of course, the evils of the convict system are similarly softened; the sort of sequences that had made I WAS A PRISONER FROM THE CHAIN GANG so powerful three years earlier are missing, and so the entire movie is softened. Perhaps it might have done better under the direction of some one other than comedy/thriller specialist Walter Forde, but I doubt it. This was not a time at which an effective movie of this sort could be made.
Despite the oddity of casting Americans in a British movie, there is little doubt that casting Veidt was a good idea. He makes the entire movie watchable, even though Beery gets to show off a sly sense humor. Miss Vinson is, alas, not up to the standards of her co-stars. Still, Veidt and Beery make this one watchable.