Jon Hall is unfortunately not a very good actor. Being invisible means that it was good not to have to see him. Watched it for Lorre, who does his Asian thing again, not surprisingly with a German accent. Those things don't matter! It's make believe!
Surprisingly effective for a Universal Monsters sequel. Aside from Bride of Frankenstein, they tended to be either retreads or (poor) parodies of their originals, but this is another exception.
Was nice to see invisibility used in a new way as well as the solid twists and turns of the wartime plot. I will say, though, that it was odd to see Peter Lorre play someone Japanese, especially with his German film roots.