Wonderfully stylish horror film, most of it a long and brilliantly gradual striptease of the protagonist bit by bit--first his hat and glasses, then his bandages, and finally his clothes. Then, in a more difficult process of unveiling, we learn of his megalomanic state of mind, which was a product of the invisibility potion, and not (as in the H.G. Wells novel, which I barely remember) a natural, psychological result of his state of invisibility.
Whales defended the change, saying he wanted a more sympathetic character; I'm not sure I agree. Still, Claude Rains' performance (mostly his voice) did suggest it was as much the man's inner desires as it was the potion that drove him mad.
I do also remember the ending was markedly different in the novel, and it was fascinating to watch this version--if one had to catch an invisible man, that's as good a way as any (the novel's method, if I recall correctly, was something of a mess). The final scene reveals Whale's total sympathy for the man, a final unveiling of intentions and appearances as the curtain draws to a close.