When someone writes a damned good novel which shines light upon the heart of humanity in all its best and worst forms, it ought to be left alone for to muck about with it is to destroy perfection. This film is smart and intelligent, and doesn’t make the mistake previously outlined.
The fact you never see the face of the main character until the very last moment of his existence is the principle reason that Boris Karloff chose not to play the role, and thus we get to hear the fabulous tones of Claude Rains instead. Thank goodness director James Whale overhead the latter actor’s screen test by accident. The voice is, quite rightly, far more important than any box-office name might normally be. The intellectual quality of the scientist who accidentally becomes invisible is key to the story being effective, for it is this which not only permits the formula to be created in the first place, it is what makes the potential of the man’s evil so much the greater.
To learn just how evil and amoral a scientist might become when reaching for the other tree in the Garden of Evil, have a look at this film. It’s exceedingly well-made, and moves along quite quickly despite my comments about the first act. You’ll likely be pleasantly surprised with the special effects, too!