I just watched the '31 Jekyll and Hyde
. It was a remarkable piece of filmmaking for its day, very technically innovative, with an impressive use of POV shots and clever transitions, particularly the recurring use of diagonal split screens to juxtapose characters and events and convey the theme of duality. I'd love to see a "making-of" featurette or article about it. Plus there were all the transformation effects, of course, and though the dissolves and jump cuts are familiar techniques today, there was one technique used that's still impressive, and that only works in black-and-white. I read about it in The Twilight Zone Companion
-- they'd paint the first stage of the transformation makeup on the actor in red (say), then light him through a red filter so it was invisible, and then they'd switch to a green filter so it would fade into view, and he would visibly begin to transform right before our eyes, purely in camera. It was done quite effectively here.
I found Hyde's makeup and behavior more comical than frightening at first, but when it got into his ongoing abusive relationship with Ivy, it became quite chilling and dark. The sexual content was pretty blatant for the era, though I guess I shouldn't be too surprised since it was pre-Code.
I also feel Hyde's appearance was given away too soon. There should've been more mystery about what was going on in that first transformation, some suspense about what the results of Jekyll's experiments were. Heck, in the original story, we didn't find out that Hyde and Jekyll were the same man until after he/they died! True, most of it was told in flashback, which was a very clumsy format for the story, but the movie could've tried to capture some of that sense of mystery.